<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>TRUNCATE</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-start-transaction.html" title="START TRANSACTION" /><link rel="next" href="sql-unlisten.html" title="UNLISTEN" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">TRUNCATE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-start-transaction.html" title="START TRANSACTION">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-unlisten.html" title="UNLISTEN">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="SQL-TRUNCATE"><div class="titlepage"></div><a id="id-1.9.3.180.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">TRUNCATE</span></h2><p>TRUNCATE — empty a table or set of tables</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
TRUNCATE [ TABLE ] [ ONLY ] <em class="replaceable"><code>name</code></em> [ * ] [, ... ]
[ RESTART IDENTITY | CONTINUE IDENTITY ] [ CASCADE | RESTRICT ]
</pre></div><div class="refsect1" id="id-1.9.3.180.5"><h2>Description</h2><p>
<code class="command">TRUNCATE</code> quickly removes all rows from a set of
tables. It has the same effect as an unqualified
<code class="command">DELETE</code> on each table, but since it does not actually
scan the tables it is faster. Furthermore, it reclaims disk space
immediately, rather than requiring a subsequent <code class="command">VACUUM</code>
operation. This is most useful on large tables.
</p></div><div class="refsect1" id="id-1.9.3.180.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of a table to truncate.
If <code class="literal">ONLY</code> is specified before the table name, only that table
is truncated. If <code class="literal">ONLY</code> is not specified, the table and all
its descendant tables (if any) are truncated. Optionally, <code class="literal">*</code>
can be specified after the table name to explicitly indicate that
descendant tables are included.
</p></dd><dt><span class="term"><code class="literal">RESTART IDENTITY</code></span></dt><dd><p>
Automatically restart sequences owned by columns of
the truncated table(s).
</p></dd><dt><span class="term"><code class="literal">CONTINUE IDENTITY</code></span></dt><dd><p>
Do not change the values of sequences. This is the default.
</p></dd><dt><span class="term"><code class="literal">CASCADE</code></span></dt><dd><p>
Automatically truncate all tables that have foreign-key references
to any of the named tables, or to any tables added to the group
due to <code class="literal">CASCADE</code>.
</p></dd><dt><span class="term"><code class="literal">RESTRICT</code></span></dt><dd><p>
Refuse to truncate if any of the tables have foreign-key references
from tables that are not listed in the command. This is the default.
</p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.180.7"><h2>Notes</h2><p>
You must have the <code class="literal">TRUNCATE</code> privilege on a table
to truncate it.
</p><p>
<code class="command">TRUNCATE</code> acquires an <code class="literal">ACCESS EXCLUSIVE</code> lock on each
table it operates on, which blocks all other concurrent operations
on the table. When <code class="literal">RESTART IDENTITY</code> is specified, any
sequences that are to be restarted are likewise locked exclusively.
If concurrent access to a table is required, then
the <code class="command">DELETE</code> command should be used instead.
</p><p>
<code class="command">TRUNCATE</code> cannot be used on a table that has foreign-key
references from other tables, unless all such tables are also truncated
in the same command. Checking validity in such cases would require table
scans, and the whole point is not to do one. The <code class="literal">CASCADE</code>
option can be used to automatically include all dependent tables —
but be very careful when using this option, or else you might lose data you
did not intend to!
</p><p>
<code class="command">TRUNCATE</code> will not fire any <code class="literal">ON DELETE</code>
triggers that might exist for the tables. But it will fire
<code class="literal">ON TRUNCATE</code> triggers.
If <code class="literal">ON TRUNCATE</code> triggers are defined for any of
the tables, then all <code class="literal">BEFORE TRUNCATE</code> triggers are
fired before any truncation happens, and all <code class="literal">AFTER
TRUNCATE</code> triggers are fired after the last truncation is
performed and any sequences are reset.
The triggers will fire in the order that the tables are
to be processed (first those listed in the command, and then any
that were added due to cascading).
</p><p>
<code class="command">TRUNCATE</code> is not MVCC-safe. After truncation, the table will
appear empty to concurrent transactions, if they are using a snapshot
taken before the truncation occurred.
See <a class="xref" href="mvcc-caveats.html" title="13.5. Caveats">Section 13.5</a> for more details.
</p><p>
<code class="command">TRUNCATE</code> is transaction-safe with respect to the data
in the tables: the truncation will be safely rolled back if the surrounding
transaction does not commit.
</p><p>
When <code class="literal">RESTART IDENTITY</code> is specified, the implied
<code class="command">ALTER SEQUENCE RESTART</code> operations are also done
transactionally; that is, they will be rolled back if the surrounding
transaction does not commit. This is unlike the normal behavior of
<code class="command">ALTER SEQUENCE RESTART</code>. Be aware that if any additional
sequence operations are done on the restarted sequences before the
transaction rolls back, the effects of these operations on the sequences
will be rolled back, but not their effects on <code class="function">currval()</code>;
that is, after the transaction <code class="function">currval()</code> will continue to
reflect the last sequence value obtained inside the failed transaction,
even though the sequence itself may no longer be consistent with that.
This is similar to the usual behavior of <code class="function">currval()</code> after
a failed transaction.
</p><p>
<code class="command">TRUNCATE</code> is not currently supported for foreign tables.
This implies that if a specified table has any descendant tables that are
foreign, the command will fail.
</p></div><div class="refsect1" id="id-1.9.3.180.8"><h2>Examples</h2><p>
Truncate the tables <code class="literal">bigtable</code> and
<code class="literal">fattable</code>:
</p><pre class="programlisting">
TRUNCATE bigtable, fattable;
</pre><p>
</p><p>
The same, and also reset any associated sequence generators:
</p><pre class="programlisting">
TRUNCATE bigtable, fattable RESTART IDENTITY;
</pre><p>
</p><p>
Truncate the table <code class="literal">othertable</code>, and cascade to any tables
that reference <code class="literal">othertable</code> via foreign-key
constraints:
</p><pre class="programlisting">
TRUNCATE othertable CASCADE;
</pre></div><div class="refsect1" id="id-1.9.3.180.9"><h2>Compatibility</h2><p>
The SQL:2008 standard includes a <code class="command">TRUNCATE</code> command
with the syntax <code class="literal">TRUNCATE TABLE
<em class="replaceable"><code>tablename</code></em></code>. The clauses
<code class="literal">CONTINUE IDENTITY</code>/<code class="literal">RESTART IDENTITY</code>
also appear in that standard, but have slightly different though related
meanings. Some of the concurrency behavior of this command is left
implementation-defined by the standard, so the above notes should be
considered and compared with other implementations if necessary.
</p></div><div class="refsect1" id="id-1.9.3.180.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-delete.html" title="DELETE"><span class="refentrytitle">DELETE</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-start-transaction.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-unlisten.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">START TRANSACTION </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> UNLISTEN</td></tr></table></div></body></html>
