truncate.sgml

来自「PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统」· SGML 代码 · 共 110 行

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$PostgreSQL: pgsql/doc/src/sgml/ref/truncate.sgml,v 1.19 2005/02/22 19:06:18 tgl Exp $
PostgreSQL documentation
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<refentry id="SQL-TRUNCATE">
 <refmeta>
  <refentrytitle id="SQL-TRUNCATE-TITLE">TRUNCATE</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>TRUNCATE</refname>
  <refpurpose>empty a table or set of tables</refpurpose>
 </refnamediv>

 <indexterm zone="sql-truncate">
  <primary>TRUNCATE</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
TRUNCATE [ TABLE ] <replaceable class="PARAMETER">name</replaceable> [, ...]
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>TRUNCATE</command> quickly removes all rows from a set of
   tables. It has the same effect as an unqualified
   <command>DELETE</command> on each table, but since it does not actually
   scan the tables it is faster. This is most useful on large tables.
  </para>
 </refsect1>
  
 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="PARAMETER">name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of a table to be truncated.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   Only the owner of a table may <command>TRUNCATE</> it.
  </para>

  <para>
   <command>TRUNCATE</> 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.
  </para>

  <para>
   <command>TRUNCATE</> will not run any user-defined <literal>ON
   DELETE</literal> triggers that might exist for the tables.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   Truncate the tables <literal>bigtable</literal> and <literal>fattable</literal>:

<programlisting>
TRUNCATE TABLE bigtable, fattable;
</programlisting>
  </para>
 </refsect1>
 
 <refsect1>
  <title>Compatibility</title>

  <para>
   There is no <command>TRUNCATE</command> command in the SQL standard.
  </para>
 </refsect1>
</refentry>

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