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<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/delete.sgml,v 1.25 2005/11/01 21:09:50 tgl Exp $
PostgreSQL documentation
-->
<refentry id="SQL-DELETE">
<refmeta>
<refentrytitle id="SQL-DELETE-TITLE">DELETE</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>DELETE</refname>
<refpurpose>delete rows of a table</refpurpose>
</refnamediv>
<indexterm zone="sql-delete">
<primary>DELETE</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
DELETE FROM [ ONLY ] <replaceable class="PARAMETER">table</replaceable>
[ USING <replaceable class="PARAMETER">usinglist</replaceable> ]
[ WHERE <replaceable class="PARAMETER">condition</replaceable> ]
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>DELETE</command> deletes rows that satisfy the
<literal>WHERE</literal> clause from the specified table. If the
<literal>WHERE</literal> clause is absent, the effect is to delete
all rows in the table. The result is a valid, but empty table.
</para>
<tip>
<para>
<xref linkend="sql-truncate" endterm="sql-truncate-title"> is a
<productname>PostgreSQL</productname> extension that provides a
faster mechanism to remove all rows from a table.
</para>
</tip>
<para>
By default, <command>DELETE</command> will delete rows in the
specified table and all its child tables. If you wish to delete only
from the specific table mentioned, you must use the
<literal>ONLY</literal> clause.
</para>
<para>
There are two ways to delete rows in a table using information
contained in other tables in the database: using sub-selects, or
specifying additional tables in the <literal>USING</literal> clause.
Which technique is more appropriate depends on the specific
circumstances.
</para>
<para>
You must have the <literal>DELETE</literal> privilege on the table
to delete from it, as well as the <literal>SELECT</literal>
privilege for any table in the <literal>USING</literal> clause or
whose values are read in the <replaceable
class="parameter">condition</replaceable>.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><literal>ONLY</></term>
<listitem>
<para>
If specified, delete rows from the named table only. When not
specified, any tables inheriting from the named table are also processed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">table</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of an existing table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">usinglist</replaceable></term>
<listitem>
<para>
A list of table expressions, allowing columns from other tables
to appear in the <literal>WHERE</> condition. This is similar
to the list of tables that can be specified in the <xref
linkend="sql-from" endterm="sql-from-title"> of a
<command>SELECT</command> statement; for example, an alias for
the table name can be specified. Do not repeat the target table
in the <replaceable class="PARAMETER">usinglist</replaceable>,
unless you wish to set up a self-join.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">condition</replaceable></term>
<listitem>
<para>
An expression returning a value of type
<type>boolean</type>, which determines the rows that are to be
deleted.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Outputs</title>
<para>
On successful completion, a <command>DELETE</> command returns a command
tag of the form
<screen>
DELETE <replaceable class="parameter">count</replaceable>
</screen>
The <replaceable class="parameter">count</replaceable> is the number
of rows deleted. If <replaceable class="parameter">count</replaceable> is
0, no rows matched the <replaceable
class="parameter">condition</replaceable> (this is not considered
an error).
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
<productname>PostgreSQL</productname> lets you reference columns of
other tables in the <literal>WHERE</> condition by specifying the
other tables in the <literal>USING</literal> clause. For example,
to delete all films produced by a given producer, one might do
<programlisting>
DELETE FROM films USING producers
WHERE producer_id = producers.id AND producers.name = 'foo';
</programlisting>
What is essentially happening here is a join between <structname>films</>
and <structname>producers</>, with all successfully joined
<structname>films</> rows being marked for deletion.
This syntax is not standard. A more standard way to do it is
<programlisting>
DELETE FROM films
WHERE producer_id IN (SELECT id FROM producers WHERE name = 'foo');
</programlisting>
In some cases the join style is easier to write or faster to
execute than the sub-select style.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Delete all films but musicals:
<programlisting>
DELETE FROM films WHERE kind <> 'Musical';
</programlisting>
</para>
<para>
Clear the table <literal>films</literal>:
<programlisting>
DELETE FROM films;
</programlisting>
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
This command conforms to the SQL standard, except that the
<literal>USING</> clause and the ability to reference other tables
in the <literal>WHERE</> clause are <productname>PostgreSQL</>
extensions.
</para>
</refsect1>
</refentry>
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