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

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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.
This commit is contained in:
Tom Lane
2006-06-26 17:24:41 +00:00
parent 4b98d423d7
commit ca0d2197ca
6 changed files with 219 additions and 26 deletions
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29
doc/src/sgml/syntax.sgml
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@ -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>
@ -1570,6 +1570,31 @@ SELECT ROW(1,2.5,'this is a test');
expression in the list.
</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
@ -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,