vpruthi/doc-exports
1
0
Fork 0
forked from docs/doc-exports
Code Pull Requests Activity
doc-exports/docs/dws/dev/dws_04_0260.html
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

110 lines
20 KiB
HTML
Raw Blame History

<a name="EN-US_TOPIC_0000001188642188"></a><a name="EN-US_TOPIC_0000001188642188"></a>
<h1 class="topictitle1">Creating a Foreign Table</h1>
<div id="body8662426"><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p12167448953">After operations in <a href="dws_04_0259.html">Creating a Foreign Server</a> are complete, create an OBS/HDFS write-only foreign table in the <span id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_ph8207163711287">GaussDB(DWS)</span> database to access data stored in OBS/HDFS. The foreign table is write-only and can be used only for data export.</p>
<div class="p" id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p33659853185314">The syntax for creating a foreign table is as follows. For details, see the syntax <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b14523144362911">CREATE FOREIGN TABLE (SQL on Hadoop or OBS)</strong>.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_screen34509377483"><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></pre></div></td><td class="code"><div><pre><span></span><span class="k">CREATE</span><span class="w"> </span><span class="k">FOREIGN</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="k">IF</span><span class="w"> </span><span class="k">NOT</span><span class="w"> </span><span class="k">EXISTS</span><span class="w"> </span><span class="p">]</span><span class="w"> </span><span class="k">table_name</span><span class="w"> </span>
<span class="p">(</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="err">{</span><span class="w"> </span><span class="k">column_name</span><span class="w"> </span><span class="n">type_name</span><span class="w"> </span>
<span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="err">{</span><span class="w"> </span><span class="p">[</span><span class="k">CONSTRAINT</span><span class="w"> </span><span class="k">constraint_name</span><span class="p">]</span><span class="w"> </span><span class="k">NULL</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="p">[</span><span class="k">CONSTRAINT</span><span class="w"> </span><span class="k">constraint_name</span><span class="p">]</span><span class="w"> </span><span class="k">NOT</span><span class="w"> </span><span class="k">NULL</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="n">column_constraint</span><span class="w"> </span><span class="p">[...]</span><span class="err">}</span><span class="w"> </span><span class="p">]</span><span class="w"> </span><span class="o">|</span>
<span class="w"> </span><span class="n">table_constraint</span><span class="w"> </span><span class="p">[,</span><span class="w"> </span><span class="p">...]</span><span class="err">}</span><span class="w"> </span><span class="p">[,</span><span class="w"> </span><span class="p">...]</span><span class="w"> </span><span class="p">]</span><span class="w"> </span><span class="p">)</span><span class="w"> </span>
<span class="w"> </span><span class="n">SERVER</span><span class="w"> </span><span class="n">dfs_server</span><span class="w"> </span>
<span class="w"> </span><span class="k">OPTIONS</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="err">{</span><span class="w"> </span><span class="n">option_name</span><span class="w"> </span><span class="s1">' value '</span><span class="w"> </span><span class="err">}</span><span class="w"> </span><span class="p">[,</span><span class="w"> </span><span class="p">...]</span><span class="w"> </span><span class="p">)</span><span class="w"> </span>
<span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="err">{</span><span class="k">WRITE</span><span class="w"> </span><span class="k">ONLY</span><span class="w"> </span><span class="err">}</span><span class="p">]</span>
<span class="w"> </span><span class="n">DISTRIBUTE</span><span class="w"> </span><span class="k">BY</span><span class="w"> </span><span class="err">{</span><span class="n">ROUNDROBIN</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">REPLICATION</span><span class="err">}</span>
<span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="n">PARTITION</span><span class="w"> </span><span class="k">BY</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="k">column_name</span><span class="w"> </span><span class="p">)</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="n">AUTOMAPPED</span><span class="w"> </span><span class="p">]</span><span class="w"> </span><span class="p">]</span><span class="w"> </span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</div>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p174842037174819">For example, when creating a foreign table named <em id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_i13661938123413">product_info_ext_obs</em>, set parameters in the syntax as follows:</p>
<ul id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_ul645584873919"><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li0456164816391"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b19458104873912">table_name</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p14459164811399">Specifies the name of the foreign table to be created.</p>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li25911413571"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b691318717383">Table column definitions</strong><ul id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_ul496273711582"><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li1446294810396"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b846619483394">column_name</strong>: specifies the name of a column in the foreign table.</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li2471194833916"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b447510488398">type_name</strong>: specifies the data type of the column.</li></ul>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p64441413214">Multiple columns are separate by commas (,).</p>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li4488164811399"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b1449034813915">SERVER dfs_server</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p114921548203913">Specifies the foreign server name of the foreign table. This server must exist. The foreign table connects to OBS/HDFS to read data through the foreign server.</p>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p1192123102315">Enter the name of the foreign server created by following steps in <a href="dws_04_0244.html">Creating a Foreign Server</a>.</p>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li184991948153914"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b450214811394">OPTIONS parameters</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p05031548113911">These are parameters associated with the foreign table. The key parameters are as follows:</p>
<ul id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_ul16505124883912"><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li86062718555"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b1924416131010">format</strong>: specifies the format of the exported data file. The ORC format is supported.</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_li976404793314"><span class="parmname" id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_parmname1592971512410"><b>foldername</b></span>: (mandatory) specifies the data source file directory in the foreign table. OBS: specifies the OBS path of the data source file. You only need to enter <strong id="EN-US_TOPIC_0000001188642188__b119547110236">/</strong><em id="EN-US_TOPIC_0000001188642188__i795431119236">Bucket name</em><strong id="EN-US_TOPIC_0000001188642188__b9954161114233">/</strong><em id="EN-US_TOPIC_0000001188642188__i2954911112318">Folder directory level</em><strong id="EN-US_TOPIC_0000001188642188__b3955711162317">/</strong>. HDFS: specifies the path in the HDFS file system. This parameter is mandatory for the write-only foreign table.</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li55231748173915"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b115261548143916">encoding</strong>: specifies the encoding of the data source file in the foreign table. The default value is <strong id="EN-US_TOPIC_0000001188642188__b658381761">utf8</strong>.</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_li1241716511227"><strong id="EN-US_TOPIC_0000001188642188__b1825442911255">filesize</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p1141934762310">Specifies the file size of a write-only foreign table, in MB. If this parameter is not specified, the file size in the distributed file system configuration is used by default. This syntax is available only for the write-only foreign table.</p>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p19846742258">Value range: an integer ranging from 1 to 1024</p>
<div class="note" id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_note32011266415"><img src="public_sys-resources/note_3.0-en-us.png"><span class="notetitle"> </span><div class="notebody"><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p02019268413">The <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b68145984511293">filesize</strong> parameter is valid only for the ORC-formatted write-only HDFS foreign table.</p>
</div></div>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_li10634202212434"><strong id="EN-US_TOPIC_0000001188642188__b92461321112420">compression</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p157219443509">(Optional) Specifies the compression mode of ORC files. This syntax is available only for the write-only foreign table.</p>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p1728715317504">Value range: <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b67764284811293">zlib</strong>, <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b203752078111293">snappy</strong>, and <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b78459629711293">lz4</strong> The default value is <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b2114596511293">snappy</strong>.</p>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_li16723183074313"><strong id="EN-US_TOPIC_0000001188642188__b59708398741325">version</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p63121479433">(Optional) Specifies the ORC version number. This syntax is available only for the write-only foreign table.</p>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p11527451104713">Value range: Only <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b187332906411293">0.12</strong> is supported. The default value is <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b155693291911293">0.12</strong>.</p>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_li1831945420718"><strong id="EN-US_TOPIC_0000001188642188__b1262873113261">dataencoding</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p11198153517818">(Optional) Specifies the data code of the data table to be exported when the database code is different from the data code of the data table. For example, the database code is Latin-1, but the data in the exported data table is in UTF-8 format. If this parameter is not specified, the database encoding format is used by default. This syntax is valid only for the write-only HDFS foreign table.</p>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p16272113181718">Value range: data code types supported by the database encoding</p>
<div class="note" id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_note1867518620215"><img src="public_sys-resources/note_3.0-en-us.png"><span class="notetitle"> </span><div class="notebody"><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_p66751367215">The <strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_b82453597711293">dataencoding</strong> parameter is valid only for the ORC-formatted write-only HDFS foreign table.</p>
</div></div>
</li></ul>
</li><li id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_li18119205351513"><strong id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_b101191753151519">Other parameters in the syntax</strong><p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p2011985361516">Other parameters are optional and can be configured as required. In this example, they do not need to be configured.</p>
<p id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_en-us_topic_0102810709_p5898193171031">Based on the preceding settings, the command for creating the foreign table is as follows:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001188642188__en-us_topic_0000001145651059_screen0768104386"><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></pre></div></td><td class="code"><div><pre><span></span><span class="k">DROP</span><span class="w"> </span><span class="k">FOREIGN</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="k">IF</span><span class="w"> </span><span class="k">EXISTS</span><span class="w"> </span><span class="n">product_info_ext_obs</span><span class="p">;</span>
<span class="c1">-- Create an OBS foreign table that does not contain partition columns. The foreign server associated with the table is obs_server, the file format on OBS corresponding to the table is ORC, and the data storage path on OBS is/mybucket/data/.</span>
<span class="k">CREATE</span><span class="w"> </span><span class="k">FOREIGN</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">product_info_ext_obs</span>
<span class="p">(</span>
<span class="w"> </span><span class="n">product_price</span><span class="w"> </span><span class="nb">integer</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_id</span><span class="w"> </span><span class="nb">char</span><span class="p">(</span><span class="mi">30</span><span class="p">)</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_time</span><span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_level</span><span class="w"> </span><span class="nb">char</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_name</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">200</span><span class="p">)</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_type1</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">20</span><span class="p">)</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_type2</span><span class="w"> </span><span class="nb">char</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_monthly_sales_cnt</span><span class="w"> </span><span class="nb">integer</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_comment_time</span><span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_comment_num</span><span class="w"> </span><span class="nb">integer</span><span class="w"> </span><span class="p">,</span>
<span class="w"> </span><span class="n">product_comment_content</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">200</span><span class="p">)</span><span class="w"> </span>
<span class="p">)</span><span class="w"> </span><span class="n">SERVER</span><span class="w"> </span><span class="n">obs_server</span><span class="w"> </span>
<span class="k">OPTIONS</span><span class="w"> </span><span class="p">(</span>
<span class="n">format</span><span class="w"> </span><span class="s1">'orc'</span><span class="p">,</span><span class="w"> </span>
<span class="n">foldername</span><span class="w"> </span><span class="s1">'/mybucket/demo.db/product_info_orc/'</span><span class="p">,</span>
<span class="w"> </span><span class="n">compression</span><span class="w"> </span><span class="s1">'snappy'</span><span class="p">,</span>
<span class="w"> </span><span class="k">version</span><span class="w"> </span><span class="s1">'0.12'</span>
<span class="p">)</span><span class="w"> </span><span class="k">Write</span><span class="w"> </span><span class="k">Only</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="dws_04_0256.html">Exporting ORC Data to OBS</a></div>
</div>
</div>
View Git Blame Copy Permalink