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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_0000001188270488"></a><a name="EN-US_TOPIC_0000001188270488"></a>
<h1 class="topictitle1">SET TRANSACTION</h1>
<div id="body8662426"><div class="section" id="EN-US_TOPIC_0000001188270488__sfa14294b9a4c44c4955b8be1eb086cf5"><h4 class="sectiontitle">Function</h4><p id="EN-US_TOPIC_0000001188270488__af6f04bf619dd4e05b7fcd87b462031c5"><strong id="EN-US_TOPIC_0000001188270488__b5938103602012">SET TRANSACTION</strong> sets the characteristics of the current transaction. It has no effect on any subsequent transactions. Available transaction characteristics include the transaction separation level and transaction access mode (read/write or read only).</p>
</div>
<div class="section" id="EN-US_TOPIC_0000001188270488__s36e9241aa4b64a27a0eceed73bc0df6b"><h4 class="sectiontitle">Precautions</h4><p id="EN-US_TOPIC_0000001188270488__a395d09ff7ded43049dcacb8b409b79ba">None</p>
</div>
<div class="section" id="EN-US_TOPIC_0000001188270488__sb7d8f214ecea4ed7bb2ba55d92b49699"><h4 class="sectiontitle">Syntax</h4><div class="p" id="EN-US_TOPIC_0000001188270488__ad617b08310bc4080b4da09043da594b8">Set the isolation level and access mode of the transaction.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001188270488__sc39bcbe5c31e4f66b1a89ff72e47918a"><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></pre></div></td><td class="code"><div><pre><span></span><span class="err">{</span><span class="w"> </span><span class="k">SET</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="k">LOCAL</span><span class="w"> </span><span class="p">]</span><span class="w"> </span><span class="k">TRANSACTION</span><span class="o">|</span><span class="k">SET</span><span class="w"> </span><span class="k">SESSION</span><span class="w"> </span><span class="k">CHARACTERISTICS</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="k">TRANSACTION</span><span class="w"> </span><span class="err">}</span>
<span class="w"> </span><span class="err">{</span><span class="w"> </span><span class="k">ISOLATION</span><span class="w"> </span><span class="k">LEVEL</span><span class="w"> </span><span class="err">{</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="k">COMMITTED</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="k">UNCOMMITTED</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">SERIALIZABLE</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">REPEATABLE</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="err">}</span>
<span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="err">{</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="k">WRITE</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="k">ONLY</span><span class="w"> </span><span class="err">}</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>
</pre></div></td></tr></table></div>
</div>
</div>
</div>
<div class="section" id="EN-US_TOPIC_0000001188270488__s5805659d3c944407854691231ec0b0f9"><h4 class="sectiontitle">Parameter Description</h4><ul id="EN-US_TOPIC_0000001188270488__u26804c32864f481cb8a8fce2ea08c08f"><li id="EN-US_TOPIC_0000001188270488__lcdb58e596f7345b9b01c428985ed54e9"><strong id="EN-US_TOPIC_0000001188270488__afb7749e3001e4907a60ac442b52e0048">LOCAL</strong><p id="EN-US_TOPIC_0000001188270488__a45a3437e8da24afab53f37d2d1959e7e">Indicates that the specified command takes effect only for the current transaction.</p>
</li><li id="EN-US_TOPIC_0000001188270488__l1d946b7cddcf4d0088dfa978465796a8"><strong id="EN-US_TOPIC_0000001188270488__ac984a255de16444b9341c0db63dd5e83">SESSION</strong><p id="EN-US_TOPIC_0000001188270488__a89918823314f439e962f3e6fe46024e5">Indicates that the specified parameters take effect for the current session.</p>
<p id="EN-US_TOPIC_0000001188270488__a5a815fc134634ad0b85c6669e330a43b">Value range: a string. It must comply with the naming convention.</p>
</li><li id="EN-US_TOPIC_0000001188270488__lf8585678a8e5440c8532fc1e5b60bf36"><strong id="EN-US_TOPIC_0000001188270488__af33231a5fda84939b27591d2daa39cec">ISOLATION LEVEL</strong><div class="p" id="EN-US_TOPIC_0000001188270488__a4ccc5e38312a4755aa9cb2eb7fddf269">Specifies the transaction isolation level that determines the data that a transaction can view if other concurrent transactions exist.<div class="note" id="EN-US_TOPIC_0000001188270488__n91a17daade7342a9bb8d5b7fe030f53b"><img src="public_sys-resources/note_3.0-en-us.png"><span class="notetitle"> </span><div class="notebody"><ul id="EN-US_TOPIC_0000001188270488__ud2a007be217447cd92b68ad07173a917"><li id="EN-US_TOPIC_0000001188270488__lf3d120573e2344de945dcf12393e4369">The isolation level of a transaction cannot be reset after the first clause (<strong id="EN-US_TOPIC_0000001188270488__b2672995895020">INSERT</strong>, <strong id="EN-US_TOPIC_0000001188270488__b3924303095020">DELETE</strong>, <strong id="EN-US_TOPIC_0000001188270488__b1764295595020">UPDATE</strong>, <strong id="EN-US_TOPIC_0000001188270488__b2456886895020">FETCH</strong>, <strong id="EN-US_TOPIC_0000001188270488__b1979322895020">COPY</strong>) for modifying data is executed in the transaction.</li></ul>
</div></div>
</div>
<p id="EN-US_TOPIC_0000001188270488__af19712cfe94f4ae083c4dedf00416755">Valid value:</p>
<ul id="EN-US_TOPIC_0000001188270488__ul4331886104528"><li id="EN-US_TOPIC_0000001188270488__li25845441104457"><strong id="EN-US_TOPIC_0000001188270488__b842352706154357">READ COMMITTED</strong>: Only committed data is read. This is the default.</li><li id="EN-US_TOPIC_0000001188270488__li24828535104518"><strong id="EN-US_TOPIC_0000001188270488__b17979182343114">READ UNCOMMITTED</strong>: <span id="EN-US_TOPIC_0000001188270488__text574277612">GaussDB(DWS)</span> does not support <strong id="EN-US_TOPIC_0000001188270488__b12959459153111">READ UNCOMMITTED</strong>. If <strong id="EN-US_TOPIC_0000001188270488__b971114817328">READ UNCOMMITTED</strong> is set, <strong id="EN-US_TOPIC_0000001188270488__b853471393211">READ COMMITTED</strong> is executed instead.</li><li id="EN-US_TOPIC_0000001188270488__li61493231104522"><strong id="EN-US_TOPIC_0000001188270488__b5453172914197">REPEATABLE READ</strong>: Only the data committed before transaction start is read. Uncommitted data or data committed in other concurrent transactions cannot be read.</li><li id="EN-US_TOPIC_0000001188270488__li26645293104525"><strong id="EN-US_TOPIC_0000001188270488__b852412434329">SERIALIZABLE</strong>: <span id="EN-US_TOPIC_0000001188270488__text604447975">GaussDB(DWS)</span> does not support <strong id="EN-US_TOPIC_0000001188270488__b201610015335">SERIALIZABLE</strong>. If <strong id="EN-US_TOPIC_0000001188270488__b15261383337">SERIALIZABLE</strong> is set, <strong id="EN-US_TOPIC_0000001188270488__b391801773311">REPEATABLE READ</strong> is executed instead.</li></ul>
</li><li id="EN-US_TOPIC_0000001188270488__le9af398f66c94012a822b81db4e51e6a"><strong id="EN-US_TOPIC_0000001188270488__ae125f4db2086415ca5c7d2da63abce5a">READ WRITE | READ ONLY</strong><p id="EN-US_TOPIC_0000001188270488__en-us_topic_0059778135_p724679911339">Specifies the transaction access mode (read/write or read only).</p>
</li></ul>
</div>
<div class="section" id="EN-US_TOPIC_0000001188270488__section159331257202518"><h4 class="sectiontitle">Examples</h4><p id="EN-US_TOPIC_0000001188270488__p1460513532297">Set the isolation level of the current transaction to <strong id="EN-US_TOPIC_0000001188270488__b199375699433521">READ COMMITTED</strong> and the access mode to <strong id="EN-US_TOPIC_0000001188270488__b147677973533521">READ ONLY</strong>:</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001188270488__screen393314577256"><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></pre></div></td><td class="code"><div><pre><span></span><span class="k">START</span><span class="w"> </span><span class="k">TRANSACTION</span><span class="p">;</span>
<span class="k">SET</span><span class="w"> </span><span class="k">LOCAL</span><span class="w"> </span><span class="k">TRANSACTION</span><span class="w"> </span><span class="k">ISOLATION</span><span class="w"> </span><span class="k">LEVEL</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="k">COMMITTED</span><span class="w"> </span><span class="k">READ</span><span class="w"> </span><span class="k">ONLY</span><span class="p">;</span>
<span class="k">COMMIT</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="dws_06_0254.html">TCL Syntax</a></div>
</div>
</div>
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