Doc patch that adds an example of a correllated UPDATE.

David Fetter

doc/src/sgml/ref/update.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.33 2005/10/12 23:19:22 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.34 2006/01/19 23:09:42 momjian Exp $
 PostgreSQL documentation
 -->
 
@@ -205,14 +205,32 @@ UPDATE employees SET sales_count = sales_count + 1 FROM accounts
   WHERE accounts.name = 'Acme Corporation'
   AND employees.id = accounts.sales_person;
 </programlisting>
+  </para>
 
+  <para>
    Perform the same operation, using a sub-select in the
    <literal>WHERE</literal> clause:
 <programlisting>
 UPDATE employees SET sales_count = sales_count + 1 WHERE id =
   (SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');
 </programlisting>
+  </para>
 
+  <para>
+   Now that all the papers are signed, update the most recently closed
+   deal of the travelling salesperson who closed the Rocket Powered
+   Skates deal with the Acme Corporation.
+<programlisting>
+UPDATE employees SET last_closed_deal = deal.id
+    FROM accounts JOIN deals ON (account.id = deal.account_id)
+    WHERE deal.employee_id = employees.id
+    AND deal.name = 'Rocket Powered Skates'
+    AND accounts.name = 'Acme Corporation'
+    ORDER BY deal.signed_date DESC LIMIT 1;
+</programlisting>
+  </para>
+
+  <para>
    Attempt to insert a new stock item along with the quantity of stock. If
    the item already exists, instead update the stock count of the existing
    item. To do this without failing the entire transaction, use savepoints.