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1 | 1 | <!-- |
2 | | -$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.20 2002/09/21 18:32:54 petere Exp $ |
| 2 | +$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.21 2003/01/06 01:20:40 tgl Exp $ |
3 | 3 | --> |
4 | 4 |
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5 | 5 | <Chapter Id="xoper"> |
@@ -472,6 +472,17 @@ table1.column1 OP table2.column2 |
472 | 472 | </itemizedlist> |
473 | 473 | </para> |
474 | 474 |
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| 475 | + <note> |
| 476 | + <para> |
| 477 | + <literal>GROUP BY</> and <literal>DISTINCT</> operations require each |
| 478 | + datatype being grouped or compared to have a mergejoinable |
| 479 | + equality operator named <literal>=</>. The equality operator and its |
| 480 | + associated <literal>SORT1</> operator are used to implement these |
| 481 | + operations. Also, the associated <literal>SORT1</> operator is the |
| 482 | + default ordering operator for <literal>ORDER BY</>. |
| 483 | + </para> |
| 484 | + </note> |
| 485 | + |
475 | 486 | <note> |
476 | 487 | <para> |
477 | 488 | In <ProductName>PostgreSQL</ProductName> versions before 7.3, |
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