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Lu, Huayi e6fa411af0 DWS DEV 830.201 version 
Reviewed-by: Pruthi, Vineet <vineet.pruthi@t-systems.com>
Co-authored-by: Lu, Huayi <luhuayi@huawei.com>
Co-committed-by: Lu, Huayi <luhuayi@huawei.com>
2024-05-16 07:24:04 +00:00

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<a name="EN-US_TOPIC_0000001587482146"></a><a name="EN-US_TOPIC_0000001587482146"></a>
<h1 class="topictitle1">Querying Joined Tables</h1>
<div id="body8662426"><div class="section" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_section10514124434714"><h4 class="sectiontitle">Join Types</h4><p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p5447954144818">Multiple joins are necessary for accomplishing complex queries. Joins are classified into inner joins and outer joins. Each type of joins have their subtypes.</p>
<ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul1129703819381"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li729763883810">Inner join: inner join, cross join, and natural join.</li><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li4297103811389">Outer join: left outer join, right outer join, and full join.</li></ul>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p544745412483">To better illustrate the differences between these joins, the following provides some examples.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p36611781319">Create the sample tables <strong id="EN-US_TOPIC_0000001587482146__b28928162173">student</strong> and <strong id="EN-US_TOPIC_0000001587482146__b28921516141719">math_score</strong> and insert data into them. Set <strong id="EN-US_TOPIC_0000001587482146__b7893191661719">enable_fast_query_shipping</strong> to <strong id="EN-US_TOPIC_0000001587482146__b3893181621716">off</strong> (<strong id="EN-US_TOPIC_0000001587482146__b1089381618174">on</strong> by default), that is, the query optimizer uses the distributed framework. Set <strong id="EN-US_TOPIC_0000001587482146__b689361618178">explain_perf_mode</strong> to <strong id="EN-US_TOPIC_0000001587482146__b78932168176">pretty</strong> (default value) to specify the <strong id="EN-US_TOPIC_0000001587482146__b10893016161715">EXPLAIN</strong> display format.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen69961469013"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">student</span><span class="p">(</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="nb">INTEGER</span><span class="p">,</span>
<span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">50</span><span class="p">)</span>
<span class="p">);</span>
<span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">math_score</span><span class="p">(</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="nb">INTEGER</span><span class="p">,</span>
<span class="w"> </span><span class="n">score</span><span class="w"> </span><span class="nb">INTEGER</span>
<span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="s1">'Tom'</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="s1">'Lily'</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="s1">'Tina'</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="s1">'Perry'</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">80</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">75</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">95</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="k">NULL</span><span class="p">);</span>
<span class="k">SET</span><span class="w"> </span><span class="n">enable_fast_query_shipping</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">off</span><span class="p">;</span>
<span class="k">SET</span><span class="w"> </span><span class="n">explain_perf_mode</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">pretty</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</div>
<div class="section" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_section931332314817"><h4 class="sectiontitle">Inner Join</h4><ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul1777012281118"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li2701858183917">Inner join<div class="p" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p5238154665"><a name="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li2701858183917"></a><a name="en-us_topic_0000001554354478_li2701858183917"></a>Syntax:<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen10847253762"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="n">left_table</span><span class="w"> </span><span class="p">[</span><span class="k">INNER</span><span class="p">]</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">right_table</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="k">ON</span><span class="w"> </span><span class="n">join_condition</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">USING</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="n">join_column</span><span class="w"> </span><span class="p">)]</span>
</pre></div></td></tr></table></div>
</div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p1884718531360">Description: Rows that meet <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b621118313324">join_condition</strong> in the left table and the right table are joined and output. Tuples that do not meet <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b149381754153217">join_condition</strong> are not output.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p4847155318614">Example 1: Query students' math scores.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen3849195313612"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span>
<span class="normal">27</span>
<span class="normal">28</span>
<span class="normal">29</span>
<span class="normal">30</span>
<span class="normal">31</span>
<span class="normal">32</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">;</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">score</span>
<span class="c1">----+-------+-------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="p">(</span><span class="mi">3</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">;</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">----------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">memory</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+-----------------------------------------+--------+----------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="w"> </span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">GATHER</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">19</span><span class="p">.</span><span class="mi">47</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="k">Join</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">11</span><span class="p">.</span><span class="mi">47</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="mi">10</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">16</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">BROADCAST</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="n">Predicate</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">---------------------------------------------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="c1">--Hash Join (3,4)</span>
<span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="n">Cond</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="o">======</span><span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">Summary</span><span class="w"> </span><span class="o">=====</span>
<span class="w"> </span><span class="c1">-------------------------------</span>
<span class="w"> </span><span class="k">System</span><span class="w"> </span><span class="n">available</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="k">Max</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">estimated</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">4400</span><span class="n">KB</span>
<span class="p">(</span><span class="mi">19</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
<ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul1536513319117"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li8110182918408">Cross join<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p2393142441513"><a name="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li8110182918408"></a><a name="en-us_topic_0000001554354478_li8110182918408"></a>Syntax:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen14151729171514"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="n">left_table</span><span class="w"> </span><span class="k">CROSS</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">right_table</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p13198436144016">Description: Each row in the left table is joined with each row in the right table. The number of final rows is the product of the number of rows on both sides. The product is also called Cartesian product.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p576622984017">Example 2: Cross join of student tables and math score tables.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen1767164911518"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span>
<span class="normal">27</span>
<span class="normal">28</span>
<span class="normal">29</span>
<span class="normal">30</span>
<span class="normal">31</span>
<span class="normal">32</span>
<span class="normal">33</span>
<span class="normal">34</span>
<span class="normal">35</span>
<span class="normal">36</span>
<span class="normal">37</span>
<span class="normal">38</span>
<span class="normal">39</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">CROSS</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="p">;</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">score</span>
<span class="c1">----+-------+-------</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tina</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tina</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tina</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tina</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="p">(</span><span class="mi">16</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">CROSS</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="p">;</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">----------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">memory</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+-----------------------------------------+--------+----------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="w"> </span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">GATHER</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">120</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">19</span><span class="p">.</span><span class="mi">89</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Nested</span><span class="w"> </span><span class="n">Loop</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">120</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">11</span><span class="p">.</span><span class="mi">89</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="mi">10</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Materialize</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">16</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">30</span>
<span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">BROADCAST</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="o">======</span><span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">Summary</span><span class="w"> </span><span class="o">=====</span>
<span class="w"> </span><span class="c1">-------------------------------</span>
<span class="w"> </span><span class="k">System</span><span class="w"> </span><span class="n">available</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="k">Max</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">estimated</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">4144</span><span class="n">KB</span>
<span class="p">(</span><span class="mi">14</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
<ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul104368381118"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li16436113814120">Natural join<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p159552389158"><a name="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li16436113814120"></a><a name="en-us_topic_0000001554354478_li16436113814120"></a>Syntax:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen148991242121517"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="n">left_table</span><span class="w"> </span><span class="k">NATURAL</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">right_table</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p22530551506">Description: Columns with the same name in left table and right table are joined by equi-join, and the columns with the same name are merged into one column.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p12531655115017">Example 3: Natural join between the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b979154013432">student </strong>table and the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1218884834315">math_score</strong> table. The columns with the same name in the two tables are the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1048061414383">id</strong> columns, therefore equivalent join is performed based on the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b175831523183810">id</strong> columns.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen172033315118"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span>
<span class="normal">27</span>
<span class="normal">28</span>
<span class="normal">29</span>
<span class="normal">30</span>
<span class="normal">31</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">NATURAL</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="p">;</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">score</span>
<span class="c1">----+-------+-------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="p">(</span><span class="mi">3</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">NATURAL</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="p">;</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">----------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">memory</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+-----------------------------------------+--------+----------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="w"> </span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">GATHER</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">19</span><span class="p">.</span><span class="mi">47</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="k">Join</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">11</span><span class="p">.</span><span class="mi">47</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="mi">10</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">16</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">BROADCAST</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="n">Predicate</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">---------------------------------------------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="c1">--Hash Join (3,4)</span>
<span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="n">Cond</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="o">======</span><span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">Summary</span><span class="w"> </span><span class="o">=====</span>
<span class="w"> </span><span class="c1">-------------------------------</span>
<span class="w"> </span><span class="k">System</span><span class="w"> </span><span class="n">available</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="k">Max</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">estimated</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">4400</span><span class="n">KB</span>
<span class="p">(</span><span class="mi">19</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
</div>
<div class="section" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_section4689105418311"><h4 class="sectiontitle">Outer Join</h4><ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul3157519919"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li1663216521197">Left Join<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p2422953131511"><a name="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li1663216521197"></a><a name="en-us_topic_0000001554354478_li1663216521197"></a>Syntax:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen13354195716157"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="n">left_table</span><span class="w"> </span><span class="k">LEFT</span><span class="w"> </span><span class="p">[</span><span class="k">OUTER</span><span class="p">]</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">right_table</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="k">ON</span><span class="w"> </span><span class="n">join_condition</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">USING</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="n">join_column</span><span class="w"> </span><span class="p">)]</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p5825161071015">Description: The result set of a left outer join includes all rows of left table, not only the joined rows. If a row in the left table does not match any row in right table, the row will be <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b14171653490">NULL</strong> in the result set.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p4213185610919">Example 4: Perform left join on the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1852162864318">student </strong>table and <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b9661203144313">math_score</strong> table. The right table data corresponding to the row where ID is 3 in the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b13627102145020">student </strong>table is filled with <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1908154175014">NULL </strong>in the result set.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen207013286104"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span>
<span class="normal">27</span>
<span class="normal">28</span>
<span class="normal">29</span>
<span class="normal">30</span>
<span class="normal">31</span>
<span class="normal">32</span>
<span class="normal">33</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">LEFT</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">);</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">score</span>
<span class="c1">----+-------+-------</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tina</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="p">(</span><span class="mi">4</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">LEFT</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">);</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">-------------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">memory</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+--------------------------------------------+--------+----------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="w"> </span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">GATHER</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="mi">26</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="k">Left</span><span class="w"> </span><span class="k">Join</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span><span class="mi">26</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">REDISTRIBUTE</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">11</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">16</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">11</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">REDISTRIBUTE</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">11</span>
<span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="n">Predicate</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">---------------------------------------------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="c1">--Hash Left Join (3, 5)</span>
<span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="n">Cond</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="o">======</span><span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">Summary</span><span class="w"> </span><span class="o">=====</span>
<span class="w"> </span><span class="c1">------------------------------</span>
<span class="w"> </span><span class="k">System</span><span class="w"> </span><span class="n">available</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">901120</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="k">Max</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">901120</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">estimated</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">7520</span><span class="n">KB</span>
<span class="p">(</span><span class="mi">20</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
<ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul117331916910"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li1243113473153">Right join<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p15399127167"><a name="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li1243113473153"></a><a name="en-us_topic_0000001554354478_li1243113473153"></a>Syntax:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen642717181612"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="n">left_table</span><span class="w"> </span><span class="k">RIGHT</span><span class="w"> </span><span class="p">[</span><span class="k">OUTER</span><span class="p">]</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">right_table</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="k">ON</span><span class="w"> </span><span class="n">join_condition</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">USING</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="n">join_column</span><span class="w"> </span><span class="p">)]</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p571015560158">Description: Contrary to the left join, the result set of a right join includes all rows of the right table, not just the joined rows. If a row in the right table does not match any row in right table, the row will be <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b4293053105713">NULL</strong> in the result set.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p18228114815157">Example 5: Perform right join on the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b128001617175813">student </strong>table and <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1080061745813">math_score</strong> table. The right table data corresponding to the row where ID is 6 in the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b10800181705815">math_score </strong>table is filled with <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b98001317115817">NULL </strong>in the result set.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen6139569161"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span>
<span class="normal">27</span>
<span class="normal">28</span>
<span class="normal">29</span>
<span class="normal">30</span>
<span class="normal">31</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">RIGHT</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">);</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">score</span>
<span class="c1">----+-------+-------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">RIGHT</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">);</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">----------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">memory</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+-----------------------------------------+--------+----------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="w"> </span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">GATHER</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">19</span><span class="p">.</span><span class="mi">47</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="k">Left</span><span class="w"> </span><span class="k">Join</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">11</span><span class="p">.</span><span class="mi">47</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="mi">10</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">16</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">BROADCAST</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">28</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="n">Predicate</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">---------------------------------------------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="c1">--Hash Left Join (3, 4)</span>
<span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="n">Cond</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="o">======</span><span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">Summary</span><span class="w"> </span><span class="o">=====</span>
<span class="w"> </span><span class="c1">-------------------------------</span>
<span class="w"> </span><span class="k">System</span><span class="w"> </span><span class="n">available</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="k">Max</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">estimated</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">5424</span><span class="n">KB</span>
<span class="p">(</span><span class="mi">19</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p3785102018418">In a right join, <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1742131686">Left</strong> is displayed in the join operator. This is because a right join is actually the process replacing the left table with the right table then performing left join.</p>
</li></ul>
<ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul3985146913"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li24081316218">Full join<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p1115222819163"><a name="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li24081316218"></a><a name="en-us_topic_0000001554354478_li24081316218"></a>Syntax:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen131623216166"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="n">left_table</span><span class="w"> </span><span class="k">FULL</span><span class="w"> </span><span class="p">[</span><span class="k">OUTER</span><span class="p">]</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">right_table</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="k">ON</span><span class="w"> </span><span class="n">join_condition</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">USING</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="n">join_column</span><span class="w"> </span><span class="p">)]</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p1772105322013">Description: A full join is a combination of a left outer join and a right outer join. The result set of a full outer join includes all rows of the left table and the right table, not just the joined rows. If a row in the left table does not match any row in the right table, the row will be <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b8922713141717">NULL</strong> in the result set. If a row in the right table does not match any row in right table, the row will be <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b5925193611719">NULL</strong> in the result set.</p>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p1679815371384">Example 6: Perform full outer join on the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1851276186">student </strong>table and <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1056576181">math_score</strong> table. The right table data corresponding to the row where ID is 3 is filled with <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1756167141818">NULL </strong>in the result set. The left table data corresponding to the row where ID is 6 is filled with <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b630825182419">NULL </strong>in the result set.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_screen169381428102112"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span>
<span class="normal">27</span>
<span class="normal">28</span>
<span class="normal">29</span>
<span class="normal">30</span>
<span class="normal">31</span>
<span class="normal">32</span>
<span class="normal">33</span>
<span class="normal">34</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">FULL</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">ON</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">);</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">score</span>
<span class="c1">----+-------+----+-------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Lily</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">75</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Perry</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">95</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tom</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">80</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">Tina</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span>
<span class="p">(</span><span class="mi">5</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">score</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="k">FULL</span><span class="w"> </span><span class="k">JOIN</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="k">ON</span><span class="w"> </span><span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="p">);</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">-------------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">memory</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+--------------------------------------------+--------+----------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="w"> </span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">GATHER</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">17</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">20</span><span class="p">.</span><span class="mi">24</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="k">Full</span><span class="w"> </span><span class="k">Join</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">17</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">12</span><span class="p">.</span><span class="mi">24</span>
<span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">REDISTRIBUTE</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">11</span><span class="p">.</span><span class="mi">06</span>
<span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">math_score</span><span class="w"> </span><span class="n">ms</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">30</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="mi">10</span>
<span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">16</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">11</span>
<span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Streaming</span><span class="p">(</span><span class="k">type</span><span class="p">:</span><span class="w"> </span><span class="n">REDISTRIBUTE</span><span class="p">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">2</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">11</span>
<span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="n">Seq</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="n">student</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="n">MB</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">01</span>
<span class="w"> </span><span class="n">Predicate</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">---------------------------------------------</span>
<span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="c1">--Hash Full Join (3, 5)</span>
<span class="w"> </span><span class="n">Hash</span><span class="w"> </span><span class="n">Cond</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">ms</span><span class="p">.</span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s</span><span class="p">.</span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="o">======</span><span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">Summary</span><span class="w"> </span><span class="o">=====</span>
<span class="w"> </span><span class="c1">-------------------------------</span>
<span class="w"> </span><span class="k">System</span><span class="w"> </span><span class="n">available</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="k">Max</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">1761280</span><span class="n">KB</span>
<span class="w"> </span><span class="n">Query</span><span class="w"> </span><span class="n">estimated</span><span class="w"> </span><span class="n">mem</span><span class="p">:</span><span class="w"> </span><span class="mi">6496</span><span class="n">KB</span>
<span class="p">(</span><span class="mi">20</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
</div>
<div class="section" id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_section1924213385298"><h4 class="sectiontitle">Differences Between the ON Condition and the WHERE Condition in Multi-Table Query</h4><p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p17985124717438">According to the preceding join syntax, except natural join and cross join, the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b89261558122612">ON</strong> condition (<strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b9554311203011">USING</strong> is converted to the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1390831683013">ON</strong> condition during query parsing) is used on the join result of both the two tables. Generally, the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b117135083114">WHERE</strong> condition is used in the query statement to restrict the query result. The <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b891602594013">ON</strong> join condition and <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b065516327406">WHERE</strong> filter condition do not contain conditions that can be pushed down to tables. The differences between <strong id="EN-US_TOPIC_0000001587482146__b1370354171620">ON</strong> and <strong id="EN-US_TOPIC_0000001587482146__b147035441613">WHERE</strong> are as follows:</p>
<ul id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_ul96651500435"><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li76658503438">The <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b11644203019464">ON</strong> condition is used for joining two tables.</li><li id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_li12665135084320"><strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b1994949134618">WHERE </strong>is used to filter the result set.</li></ul>
<p id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_p194461242162910">To sum up, the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b191879085416">ON</strong> condition is used when two tables are joined. After the join result set of two tables is generated, the <strong id="EN-US_TOPIC_0000001587482146__en-us_topic_0000001554354478_b251455011541">WHERE</strong> condition is used.</p>
</div>
</div>
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