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Add a specific example of parenthesizing when extracting a field of a

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composite column.  Might help cut down on future questions...
This commit is contained in:
Tom Lane
2008-12-09 20:52:03 +00:00
parent dea81a6cf6
commit 5932915fef
1 changed files with 13 additions and 2 deletions
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15
doc/src/sgml/syntax.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.125 2008/10/29 14:35:04 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.126 2008/12/09 20:52:03 tgl Exp $ -->
<chapter id="sql-syntax">
<title>SQL Syntax</title>
@@ -1387,7 +1387,18 @@ $1.somecolumn
</programlisting>
(Thus, a qualified column reference is actually just a special case
of the field selection syntax.)
of the field selection syntax.) An important special case is
extracting a field from a table column that is of a composite type:
<programlisting>
(compositecol).somefield
(mytable.compositecol).somefield
</programlisting>
The parentheses are required here to show that
<structfield>compositecol</> is a column name not a table name,
or that <structname>mytable</> is a table name not a schema name
in the second case.
</para>
</sect2>