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1 |
| -<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.125 2008/10/29 14:35:04 momjian Exp $ --> |
| 1 | +<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.126 2008/12/09 20:52:03 tgl Exp $ --> |
2 | 2 |
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3 | 3 | <chapter id="sql-syntax">
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4 | 4 | <title>SQL Syntax</title>
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@@ -1387,7 +1387,18 @@ $1.somecolumn
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1387 | 1387 | </programlisting>
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1388 | 1388 |
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1389 | 1389 | (Thus, a qualified column reference is actually just a special case
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1390 |
| - of the field selection syntax.) |
| 1390 | + of the field selection syntax.) An important special case is |
| 1391 | + extracting a field from a table column that is of a composite type: |
| 1392 | + |
| 1393 | +<programlisting> |
| 1394 | +(compositecol).somefield |
| 1395 | +(mytable.compositecol).somefield |
| 1396 | +</programlisting> |
| 1397 | + |
| 1398 | + The parentheses are required here to show that |
| 1399 | + <structfield>compositecol</> is a column name not a table name, |
| 1400 | + or that <structname>mytable</> is a table name not a schema name |
| 1401 | + in the second case. |
1391 | 1402 | </para>
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1392 | 1403 | </sect2>
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1393 | 1404 |
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