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1 | 1 | <!-- |
2 | | -$PostgreSQL: pgsql/doc/src/sgml/ref/create_table.sgml,v 1.80 2004/03/22 16:18:50 tgl Exp $ |
| 2 | +$PostgreSQL: pgsql/doc/src/sgml/ref/create_table.sgml,v 1.81 2004/05/19 23:10:43 momjian Exp $ |
3 | 3 | PostgreSQL documentation |
4 | 4 | --> |
5 | 5 |
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@@ -383,10 +383,13 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: |
383 | 383 | <para> |
384 | 384 | The <literal>CHECK</> clause specifies an expression producing a |
385 | 385 | Boolean result which new or updated rows must satisfy for an |
386 | | - insert or update operation to succeed. A check constraint |
387 | | - specified as a column constraint should reference that column's |
388 | | - value only, while an expression appearing in a table constraint |
389 | | - may reference multiple columns. |
| 386 | + insert or update operation to succeed. Expressions evaluating |
| 387 | + to TRUE or UNKNOWN succeed. Should any row of an insert or |
| 388 | + update operation produce a FALSE result an error exception is |
| 389 | + raised and the insert or update does not alter the database. A |
| 390 | + check constraint specified as a column constraint should |
| 391 | + reference that column's value only, while an expression |
| 392 | + appearing in a table constraint may reference multiple columns. |
390 | 393 | </para> |
391 | 394 |
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392 | 395 | <para> |
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