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and DELETE. If specified, the alias must be used instead of the full table name. Also, the alias currently cannot be used in the SET clause of UPDATE. Patch from Atsushi Ogawa, various editorialization by Neil Conway. Along the way, make the rowtypes regression test pass if add_missing_from is enabled, and add a new (skeletal) regression test for DELETE.
303 lines
9.5 KiB
Plaintext
303 lines
9.5 KiB
Plaintext
<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.35 2006/01/22 05:20:33 neilc Exp $
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PostgreSQL documentation
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-->
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<refentry id="SQL-UPDATE">
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<refmeta>
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<refentrytitle id="SQL-UPDATE-TITLE">UPDATE</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>UPDATE</refname>
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<refpurpose>update rows of a table</refpurpose>
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</refnamediv>
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<indexterm zone="sql-update">
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<primary>UPDATE</primary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
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SET <replaceable class="PARAMETER">column</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...]
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[ FROM <replaceable class="PARAMETER">fromlist</replaceable> ]
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[ WHERE <replaceable class="PARAMETER">condition</replaceable> ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>UPDATE</command> changes the values of the specified
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columns in all rows that satisfy the condition. Only the columns to
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be modified need be mentioned in the <literal>SET</literal> clause;
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columns not explicitly modified retain their previous values.
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</para>
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<para>
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By default, <command>UPDATE</command> will update rows in the
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specified table and all its subtables. If you wish to only update
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the specific table mentioned, you must use the <literal>ONLY</>
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clause.
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</para>
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<para>
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There are two ways to modify a table using information contained in
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other tables in the database: using sub-selects, or specifying
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additional tables in the <literal>FROM</literal> clause. Which
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technique is more appropriate depends on the specific
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circumstances.
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</para>
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<para>
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You must have the <literal>UPDATE</literal> privilege on the table
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to update it, as well as the <literal>SELECT</literal>
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privilege to any table whose values are read in the
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<replaceable class="parameter">expression</replaceable>s or
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<replaceable class="parameter">condition</replaceable>.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><replaceable class="PARAMETER">table</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of the table to update.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">alias</replaceable></term>
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<listitem>
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<para>
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A substitute name for the target table. When an alias is
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provided, it completely hides the actual name of the table. For
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example, given <literal>UPDATE foo AS f</>, the remainder of the
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<command>UPDATE</command> statement must refer to this table as
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<literal>f</> not <literal>foo</>. You cannot use the alias in
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the <literal>SET</literal> clause. For example, <literal>SET
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f.col = 1</> is invalid.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="PARAMETER">column</replaceable></term>
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<listitem>
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<para>
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The name of a column in <replaceable
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class="PARAMETER">table</replaceable>.
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The column name can be qualified with a subfield name or array
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subscript, if needed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="PARAMETER">expression</replaceable></term>
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<listitem>
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<para>
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An expression to assign to the column. The expression may use the
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old values of this and other columns in the table.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>DEFAULT</literal></term>
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<listitem>
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<para>
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Set the column to its default value (which will be NULL if no
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specific default expression has been assigned to it).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="PARAMETER">fromlist</replaceable></term>
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<listitem>
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<para>
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A list of table expressions, allowing columns from other tables
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to appear in the <literal>WHERE</> condition and the update
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expressions. This is similar to the list of tables that can be
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specified in the <xref linkend="sql-from"
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endterm="sql-from-title"> of a <command>SELECT</command>
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statement. Note that the target table must not appear in the
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<replaceable>fromlist</>, unless you intend a self-join (in which
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case it must appear with an alias in the <replaceable>fromlist</>).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="PARAMETER">condition</replaceable></term>
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<listitem>
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<para>
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An expression that returns a value of type <type>boolean</type>.
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Only rows for which this expression returns <literal>true</>
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will be updated.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Outputs</title>
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<para>
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On successful completion, an <command>UPDATE</> command returns a command
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tag of the form
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<screen>
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UPDATE <replaceable class="parameter">count</replaceable>
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</screen>
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The <replaceable class="parameter">count</replaceable> is the number
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of rows updated. If <replaceable class="parameter">count</replaceable> is
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0, no rows matched the <replaceable
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class="parameter">condition</replaceable> (this is not considered
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an error).
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</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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When a <literal>FROM</> clause is present, what essentially happens
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is that the target table is joined to the tables mentioned in the
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<replaceable>fromlist</replaceable>, and each output row of the join
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represents an update operation for the target table. When using
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<literal>FROM</> you should ensure that the join
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produces at most one output row for each row to be modified. In
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other words, a target row shouldn't join to more than one row from
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the other table(s). If it does, then only one of the join rows
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will be used to update the target row, but which one will be used
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is not readily predictable.
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</para>
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<para>
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Because of this indeterminacy, referencing other tables only within
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sub-selects is safer, though often harder to read and slower than
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using a join.
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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Change the word <literal>Drama</> to <literal>Dramatic</> in the
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column <structfield>kind</> of the table <structname>films</structname>:
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<programlisting>
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UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
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</programlisting>
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</para>
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<para>
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Adjust temperature entries and reset precipitation to its default
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value in one row of the table <structname>weather</structname>:
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<programlisting>
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UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
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WHERE city = 'San Francisco' AND date = '2003-07-03';
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</programlisting>
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</para>
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<para>
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Increment the sales count of the salesperson who manages the
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account for Acme Corporation, using the <literal>FROM</literal>
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clause syntax:
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<programlisting>
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UPDATE employees SET sales_count = sales_count + 1 FROM accounts
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WHERE accounts.name = 'Acme Corporation'
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AND employees.id = accounts.sales_person;
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</programlisting>
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</para>
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<para>
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Perform the same operation, using a sub-select in the
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<literal>WHERE</literal> clause:
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<programlisting>
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UPDATE employees SET sales_count = sales_count + 1 WHERE id =
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(SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');
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</programlisting>
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</para>
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<para>
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Now that all the papers are signed, update the most recently closed
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deal of the travelling salesperson who closed the Rocket Powered
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Skates deal with the Acme Corporation.
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<programlisting>
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UPDATE employees SET last_closed_deal = deal.id
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FROM accounts JOIN deals ON (account.id = deal.account_id)
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WHERE deal.employee_id = employees.id
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AND deal.name = 'Rocket Powered Skates'
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AND accounts.name = 'Acme Corporation'
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ORDER BY deal.signed_date DESC LIMIT 1;
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</programlisting>
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</para>
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<para>
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Attempt to insert a new stock item along with the quantity of stock. If
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the item already exists, instead update the stock count of the existing
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item. To do this without failing the entire transaction, use savepoints.
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<programlisting>
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BEGIN;
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-- other operations
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SAVEPOINT sp1;
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INSERT INTO wines VALUES('Chateau Lafite 2003', '24');
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-- Assume the above fails because of a unique key violation,
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-- so now we issue these commands:
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ROLLBACK TO sp1;
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UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003';
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-- continue with other operations, and eventually
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COMMIT;
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</programlisting>
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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This command conforms to the <acronym>SQL</acronym> standard, except
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that the <literal>FROM</literal> clause is a
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<productname>PostgreSQL</productname> extension.
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</para>
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<para>
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Some other database systems offer a <literal>FROM</> option in which
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the target table is supposed to be listed again within <literal>FROM</>.
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That is not how <productname>PostgreSQL</productname> interprets
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<literal>FROM</>. Be careful when porting applications that use this
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extension.
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:nil
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../reference.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:"/usr/lib/sgml/catalog"
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sgml-local-ecat-files:nil
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End:
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-->
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