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<title>Truncate (SQL)</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Truncate (SQL)</span></span>

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<p>In <a href="SQL" title="SQL">SQL</a>, the <b><code>TRUNCATE TABLE</code></b> statement is a <a href="Data_manipulation_language" title="Data manipulation language">data manipulation language</a> (DML)<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> operation that deletes all rows of a table without causing a triggered action. The result of this operation quickly removes all data from a <a href="Table_(database)" title="Table (database)">table</a>, typically bypassing a number of integrity enforcing mechanisms. It was officially introduced in the <a href="SQL%3A2008" title="SQL:2008">SQL:2008</a> standard, as the optional feature F200, "TRUNCATE TABLE statement".

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<div class="mw-heading mw-heading2"><h2 id="Behavior">Behavior</h2></div>

<p>TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes, and so on remain. To remove the table definition in addition to its data, use the <a href="Data_definition_language#DROP_statement" title="Data definition language">DROP TABLE</a> statement.

</p><p>The <code>TRUNCATE TABLE mytable</code> statement is logically (though not physically) equivalent to the <code><a href="Delete_(SQL)" title="Delete (SQL)">DELETE</a> FROM mytable</code> statement (without a <code>WHERE</code> clause). The following characteristics distinguish <code>TRUNCATE TABLE</code> from <code>DELETE</code>:

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<ul><li>In the <a href="Oracle_Database" title="Oracle Database">Oracle Database</a>, <code>TRUNCATE</code> is implicitly preceded and followed by a <a href="Commit_(data_management)" title="Commit (data management)">commit</a> operation. (This may also be the case in <a href="MySQL" title="MySQL">MySQL</a>, when using a transactional storage engine.)</li>

<li>Typically, <code>TRUNCATE TABLE</code> quickly deletes all records in a table by deallocating the data pages used by the table. This reduces the resource overhead of <a href="Transaction_log" title="Transaction log">logging</a> the deletions, as well as the number of <a href="Lock_(database)" class="mw-redirect" title="Lock (database)">locks</a> acquired. Records removed this way cannot be restored in a rollback operation. Two notable exceptions to this rule are the implementations found in <a href="PostgreSQL" title="PostgreSQL">PostgreSQL</a> and <a href="Microsoft_SQL_Server" title="Microsoft SQL Server">Microsoft SQL Server</a>, both of which allow <code>TRUNCATE TABLE</code> statements to be committed or rolled back transactionally.</li>

<li>It is not possible to specify a <code>WHERE</code> clause in a <code>TRUNCATE TABLE</code> statement.</li>

<li><code>TRUNCATE TABLE</code> cannot be used when a foreign key references the table to be truncated, since <code>TRUNCATE TABLE</code> statements do not fire <a href="Database_trigger" title="Database trigger">triggers</a>. This could result in inconsistent data because <code>ON DELETE</code>/<code>ON UPDATE</code> triggers would not fire.</li>

<li>In some computer systems, <code>TRUNCATE TABLE</code> resets the count of an <a href="Identity_column" title="Identity column">Identity column</a> back to the identity's <i>seed</i>.</li></ul>

<p>The SQL standard classifies TRUNCATE as a <i>data change statement</i>, synonymous with data manipulation (DML). This aligns with TRUNCATE being logically equivalent to an unconstrained DELETE operation.

</p><p>However, some documents describe TRUNCATE as a <a href="Data_definition_language" title="Data definition language">data definition language</a> (DDL) operation, because TRUNCATE may be seen as a combined DROP+CREATE operation.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">The <a href="Backus-Naur_form" class="mw-redirect" title="Backus-Naur form">BNF</a> for SQL:2023 defines TRUNCATE as an SQL data change statement: <style data-mw-deduplicate="TemplateStyles:r1238218222">

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</style><cite id="ISO/IEC_9075-2" class="citation web cs1"><a rel="nofollow" class="external text" href="https://standards.iso.org/iso-iec/9075/-2/ed-6/en/ISO_IEC_9075-2(E)_Foundation.bnf.txt">"ISO/IEC 9075 BNF"</a>. <i>iso.org</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2024-12-30</span></span>.</cite></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">For example, MySQL's documentation classifies TRUNCATE as a DDL statement: <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://dev.mysql.com/doc/refman/8.4/en/truncate-table.html">"MySQL :: MySQL 8.4 Reference Manual :: 15.1.37 TRUNCATE TABLE Statement"</a>. <i>dev.mysql.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2024-12-30</span></span>.</cite></span>

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</style><div id="SQL70" style="font-size:114%;margin:0 4em"><a href="SQL" title="SQL">SQL</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Versions</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="SEQUEL" class="mw-redirect" title="SEQUEL">SEQUEL</a></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="SQL_reserved_words" class="mw-redirect" title="SQL reserved words">Keywords</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><span class="smallcaps"><a href="Create_(SQL)" class="mw-redirect" title="Create (SQL)">Create</a></span></li>

<li><span class="smallcaps"><a href="Delete_(SQL)" title="Delete (SQL)">Delete</a></span></li>

<li><span class="smallcaps"><a href="Group_by_(SQL)" title="Group by (SQL)">Group by</a></span></li>

<li><span class="smallcaps"><a href="Having_(SQL)" title="Having (SQL)">Having</a></span></li>

<li><span class="smallcaps"><a href="Insert_(SQL)" title="Insert (SQL)">Insert</a></span></li>

<li><span class="smallcaps"><a href="Merge_(SQL)" title="Merge (SQL)">Merge</a></span></li>

<li><span class="smallcaps"><a href="Order_by" title="Order by">Order by</a></span></li>

<li><span class="smallcaps"><a href="Prepare_(SQL)" class="mw-redirect" title="Prepare (SQL)">Prepare</a></span></li>

<li><span class="smallcaps"><a href="Select_(SQL)" title="Select (SQL)">Select</a></span></li>

<li><span class="smallcaps"><a href="Set_operations_(SQL)" title="Set operations (SQL)">Union</a></span></li>

<li><span class="smallcaps"><a href="Update_(SQL)" title="Update (SQL)">Update</a></span></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Edgar_F._Codd" title="Edgar F. Codd">Edgar Codd</a></li>

<li><a href="Relational_database" title="Relational database">Relational database</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">ISO/IEC SQL parts</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li>Framework</li>

<li>Foundation</li>

<li><a href="SQL/CLI" class="mw-redirect" title="SQL/CLI">Call-Level Interface</a></li>

<li><a href="SQL/PSM" title="SQL/PSM">Persistent Stored Modules</a></li>

<li><a href="SQL/MED" title="SQL/MED">Management of External Data</a></li>

<li><a href="SQL/OLB" title="SQL/OLB">Object Language Bindings</a></li>

<li><a href="SQL/Schemata" title="SQL/Schemata">Information and Definition Schemas</a></li>

<li><a href="SQL/JRT" title="SQL/JRT">SQL Routines and Types for the Java Programming Language</a></li>

<li><a href="SQL/XML" title="SQL/XML">XML-Related Specifications</a></li></ul>

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