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<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.27 2003/11/29 19:51:39 pgsql Exp $
PostgreSQL documentation
-->
<refentry id="SQL-UPDATE">
<refmeta>
<refentrytitle id="SQL-UPDATE-TITLE">UPDATE</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>UPDATE</refname>
<refpurpose>update rows of a table</refpurpose>
</refnamediv>
<indexterm zone="sql-update">
<primary>UPDATE</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replaceable class="PARAMETER">column</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...]
[ FROM <replaceable class="PARAMETER">fromlist</replaceable> ]
[ WHERE <replaceable class="PARAMETER">condition</replaceable> ]
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>UPDATE</command> changes the values of the specified
columns in all rows that satisfy the condition. Only the columns to
be modified need be mentioned in the statement; columns not explicitly
<literal>SET</> retain their previous values.
</para>
<para>
By default, <command>UPDATE</command> will update rows in the
specified table and all its subtables. If you wish to only update
the specific table mentioned, you must use the <literal>ONLY</>
clause.
</para>
<para>
You must have the <literal>UPDATE</literal> privilege on the table
to update it, as well as the <literal>SELECT</literal>
privilege to any table whose values are read in the
<replaceable class="parameter">expression</replaceable>s or
<replaceable class="parameter">condition</replaceable>.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER">table</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of the table to update.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">column</replaceable></term>
<listitem>
<para>
The name of a column in <replaceable class="PARAMETER">table</replaceable>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">expression</replaceable></term>
<listitem>
<para>
An expression to assign to the column. The expression may use the
old values of this and other columns in the table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DEFAULT</literal></term>
<listitem>
<para>
Set the column to its default value (which will be NULL if no
specific default expression has been assigned to it).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">fromlist</replaceable></term>
<listitem>
<para>
A list of table expressions, allowing columns from other tables
to appear in the <literal>WHERE</> condition and the update expressions.
</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</>
will be updated.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Outputs</title>
<para>
On successful completion, an <command>UPDATE</> command returns a command
tag of the form
<screen>
UPDATE <replaceable class="parameter">count</replaceable>
</screen>
The <replaceable class="parameter">count</replaceable> is the number
of rows updated. 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>Examples</title>
<para>
Change the word <literal>Drama</> to <literal>Dramatic</> in the
column <structfield>kind</> of the table <literal>films</literal>:
<programlisting>
UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
</programlisting>
</para>
<para>
Adjust temperature entries and reset precipitation to its default
value in one row of the table <literal>weather</literal>:
<programlisting>
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
WHERE city = 'San Francisco' AND date = '2003-07-03';
</programlisting>
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
This command conforms to the SQL standard. The
<literal>FROM</literal> clause is a
<productname>PostgreSQL</productname> extension.
</para>
</refsect1>
</refentry>
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