Change the row constructor syntax (ROW(...)) so that list elements foo.*

will be expanded to a list of their member fields, rather than creating
a nested rowtype field as formerly.  (The old behavior is still available
by omitting '.*'.)  This syntax is not allowed by the SQL spec AFAICS,
so changing its behavior doesn't violate the spec.  The new behavior is
substantially more useful since it allows, for example, triggers to check
for data changes with 'if row(new.*) is distinct from row(old.*)'.  Per
my recent proposal.

1 files changed, 27 insertions, 2 deletions

diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 97020845b50..74cc813a681 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.106 2006/03/10 19:10:49 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.107 2006/06/26 17:24:40 tgl Exp $ -->
 
 <chapter id="sql-syntax">
  <title>SQL Syntax</title>
@@ -1571,6 +1571,31 @@ SELECT ROW(1,2.5,'this is a test');
    </para>
 
    <para>
+    A row constructor can include the syntax
+    <replaceable>rowvalue</replaceable><literal>.*</literal>,
+    which will be expanded to a list of the elements of the row value,
+    just as occurs when the <literal>.*</> syntax is used at the top level
+    of a <command>SELECT</> list.  For example, if table <literal>t</> has
+    columns <literal>f1</> and <literal>f2</>, these are the same:
+<programlisting>
+SELECT ROW(t.*, 42) FROM t;
+SELECT ROW(t.f1, t.f2, 42) FROM t;
+</programlisting>
+   </para>
+
+   <note>
+    <para>
+     Before <productname>PostgreSQL</productname> 8.2, the
+     <literal>.*</literal> syntax was not expanded, so that writing
+     <literal>ROW(t.*, 42)</> created a two-field row whose first field
+     was another row value.  The new behavior is usually more useful.
+     If you need the old behavior of nested row values, write the inner
+     row value without <literal>.*</literal>, for instance
+     <literal>ROW(t, 42)</>.
+    </para>
+   </note>
+
+   <para>
     By default, the value created by a <literal>ROW</> expression is of
     an anonymous record type.  If necessary, it can be cast to a named
     composite type &mdash; either the row type of a table, or a composite type
@@ -1619,7 +1644,7 @@ SELECT getf1(CAST(ROW(11,'this is a test',2.5) AS myrowtype));
 <programlisting>
 SELECT ROW(1,2.5,'this is a test') = ROW(1, 3, 'not the same');
 
-SELECT ROW(a, b, c) IS NOT NULL FROM table;
+SELECT ROW(table.*) IS NULL FROM table;  -- detect all-null rows
 </programlisting>
    For more detail see <xref linkend="functions-comparisons">.
    Row constructors can also be used in connection with subqueries,