From 091fe037757abbecd6994daea0ae4eaa87f7217e Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 3 Sep 2006 22:37:06 +0000
Subject: Code review for UPDATE SET (columnlist) patch.  Make it handle as
 much of the syntax as this fundamentally dead-end approach can, in particular
 combinations of single and multi column assignments.  Improve rather
 inadequate documentation and provide some regression tests.

---
 doc/src/sgml/ref/update.sgml | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/ref/update.sgml b/doc/src/sgml/ref/update.sgml
index 7b5d17a1fc8..ec2200f3bc9 100644
--- a/doc/src/sgml/ref/update.sgml
+++ b/doc/src/sgml/ref/update.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.39 2006/09/02 20:34:47 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.40 2006/09/03 22:37:05 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -21,8 +21,8 @@ PostgreSQL documentation
  <refsynopsisdiv>
 <synopsis>
 UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
-    [ SET <replaceable class="PARAMETER">column</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] |
-      SET ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) = ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) [, ...] ]
+    SET { <replaceable class="PARAMETER">column</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } |
+          ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) = ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) } [, ...]
     [ FROM <replaceable class="PARAMETER">fromlist</replaceable> ]
     [ WHERE <replaceable class="PARAMETER">condition</replaceable> ]
     [ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ AS <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
@@ -251,10 +251,6 @@ UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
 <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>
-<programlisting>
-UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT)
-  WHERE city = 'San Francisco' AND date = '2003-07-03';
 </programlisting>
   </para>
 
@@ -268,6 +264,14 @@ UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
 </programlisting>
   </para>
 
+  <para>
+   Use the alternative column-list syntax to do the same update:
+<programlisting>
+UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT)
+  WHERE city = 'San Francisco' AND date = '2003-07-03';
+</programlisting>
+  </para>
+
   <para>
    Increment the sales count of the salesperson who manages the
    account for Acme Corporation, using the <literal>FROM</literal>
@@ -316,6 +320,19 @@ COMMIT;
    are <productname>PostgreSQL</productname> extensions.
   </para>
 
+  <para>
+   According to the standard, the column-list syntax should allow a list
+   of columns to be assigned from a single row-valued expression, such
+   as a sub-select:
+<programlisting>
+UPDATE accounts SET (contact_last_name, contact_first_name) =
+    (SELECT last_name, first_name FROM salesmen
+     WHERE salesmen.id = accounts.sales_id);
+</programlisting>
+   This is not currently implemented &mdash; the source must be a list
+   of independent expressions.
+  </para>
+
   <para>
    Some other database systems offer a <literal>FROM</> option in which
    the target table is supposed to be listed again within <literal>FROM</>.
-- 
cgit v1.2.3