postgresql/doc/src/sgml/ref/delete.sgml

<!--
doc/src/sgml/ref/delete.sgml
PostgreSQL documentation
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<refentry id="sql-delete">
 <indexterm zone="sql-delete">
  <primary>DELETE</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>DELETE</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>DELETE</refname>
  <refpurpose>delete rows of a table</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
[ WITH [ RECURSIVE ] <replaceable class="parameter">with_query</replaceable> [, ...] ]
DELETE FROM [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ] [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
    [ USING <replaceable class="parameter">from_item</replaceable> [, ...] ]
    [ WHERE <replaceable class="parameter">condition</replaceable> | WHERE CURRENT OF <replaceable class="parameter">cursor_name</replaceable> ]
    [ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</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>
     <link linkend="sql-truncate"><command>TRUNCATE</command></link> provides a
     faster mechanism to remove all rows from a table.
    </para>
   </tip>

  <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>
   The optional <literal>RETURNING</literal> clause causes <command>DELETE</command>
   to compute and return value(s) based on each row actually deleted.
   Any expression using the table's columns, and/or columns of other
   tables mentioned in <literal>USING</literal>, can be computed.
   The syntax of the <literal>RETURNING</literal> list is identical to that of the
   output list of <command>SELECT</command>.
  </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><replaceable class="parameter">with_query</replaceable></term>
    <listitem>
     <para>
      The <literal>WITH</literal> clause allows you to specify one or more
      subqueries that can be referenced by name in the <command>DELETE</command>
      query. See <xref linkend="queries-with"/> and <xref linkend="sql-select"/>
      for details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">table_name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the table to delete rows
      from.  If <literal>ONLY</literal> is specified before the table name,
      matching rows are deleted from the named table only.  If
      <literal>ONLY</literal> is not specified, matching rows are also deleted
      from any tables inheriting from the named table.  Optionally,
      <literal>*</literal> can be specified after the table name to explicitly
      indicate that descendant tables are included.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">alias</replaceable></term>
    <listitem>
     <para>
      A substitute name for the target table. When an alias is
      provided, it completely hides the actual name of the table.  For
      example, given <literal>DELETE FROM foo AS f</literal>, the remainder
      of the <command>DELETE</command> statement must refer to this
      table as <literal>f</literal> not <literal>foo</literal>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">from_item</replaceable></term>
    <listitem>
     <para>
      A table expression allowing columns from other tables to appear
      in the <literal>WHERE</literal> condition.  This uses the same
      syntax as the <link linkend="sql-from"><literal>FROM</literal></link>
      clause of a <command>SELECT</command> statement; for example, an alias
      for the table name can be specified.  Do not repeat the target
      table as a <replaceable class="parameter">from_item</replaceable>
      unless you wish to set up a self-join (in which case it must appear
      with an alias in the <replaceable>from_item</replaceable>).
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">condition</replaceable></term>
    <listitem>
     <para>
      An expression that returns a value of type <type>boolean</type>.
      Only rows for which this expression returns <literal>true</literal>
      will be deleted.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">cursor_name</replaceable></term>
    <listitem>
     <para>
      The name of the cursor to use in a <literal>WHERE CURRENT OF</literal>
      condition.  The row to be deleted is the one most recently fetched
      from this cursor.  The cursor must be a non-grouping
      query on the <command>DELETE</command>'s target table.
      Note that <literal>WHERE CURRENT OF</literal> cannot be
      specified together with a Boolean condition.  See
      <xref linkend="sql-declare"/>
      for more information about using cursors with
      <literal>WHERE CURRENT OF</literal>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">output_expression</replaceable></term>
    <listitem>
     <para>
      An expression to be computed and returned by the <command>DELETE</command>
      command after each row is deleted.  The expression can use any
      column names of the table named by <replaceable class="parameter">table_name</replaceable>
      or table(s) listed in <literal>USING</literal>.
      Write <literal>*</literal> to return all columns.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">output_name</replaceable></term>
    <listitem>
     <para>
      A name to use for a returned column.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Outputs</title>

  <para>
   On successful completion, a <command>DELETE</command> 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.  Note that the number may be less than the number of
   rows that matched the <replaceable
   class="parameter">condition</replaceable> when deletes were
   suppressed by a <literal>BEFORE DELETE</literal> trigger.  If <replaceable
   class="parameter">count</replaceable> is 0, no rows were deleted by
   the query (this is not considered an error).
  </para>

  <para>
   If the <command>DELETE</command> command contains a <literal>RETURNING</literal>
   clause, the result will be similar to that of a <command>SELECT</command>
   statement containing the columns and values defined in the
   <literal>RETURNING</literal> list, computed over the row(s) deleted by the
   command.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <productname>PostgreSQL</productname> lets you reference columns of
   other tables in the <literal>WHERE</literal> condition by specifying the
   other tables in the <literal>USING</literal> clause.  For example,
   to delete all films produced by a given producer, one can 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</structname>
   and <structname>producers</structname>, with all successfully joined
   <structname>films</structname> 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 &lt;&gt; 'Musical';
</programlisting>
  </para>

  <para>
   Clear the table <literal>films</literal>:
<programlisting>
DELETE FROM films;
</programlisting>
  </para>

  <para>
   Delete completed tasks, returning full details of the deleted rows:
<programlisting>
DELETE FROM tasks WHERE status = 'DONE' RETURNING *;
</programlisting>
  </para>

  <para>
   Delete the row of <structname>tasks</structname> on which the cursor
   <literal>c_tasks</literal> is currently positioned:
<programlisting>
DELETE FROM tasks WHERE CURRENT OF c_tasks;
</programlisting>
  </para>

  <para>
   While there is no <literal>LIMIT</literal> clause
   for <command>DELETE</command>, it is possible to get a similar effect
   using the same method described in <link linkend="update-limit">the
   documentation of <command>UPDATE</command></link>:
<programlisting>
WITH delete_batch AS (
  SELECT l.ctid FROM user_logs AS l
    WHERE l.status = 'archived'
    ORDER BY l.creation_date
    FOR UPDATE
    LIMIT 10000
)
DELETE FROM user_logs AS dl
  USING delete_batch AS del
  WHERE dl.ctid = del.ctid;
</programlisting>
  </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   This command conforms to the <acronym>SQL</acronym> standard, except
   that the <literal>USING</literal> and <literal>RETURNING</literal> clauses
   are <productname>PostgreSQL</productname> extensions, as is the ability
   to use <literal>WITH</literal> with <command>DELETE</command>.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-truncate"/></member>
  </simplelist>
 </refsect1>
</refentry>