diff options
Diffstat (limited to 'doc/src/sgml/ref/alter_table.sgml')
| -rw-r--r-- | doc/src/sgml/ref/alter_table.sgml | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml index 890b23afd64..e360728c025 100644 --- a/doc/src/sgml/ref/alter_table.sgml +++ b/doc/src/sgml/ref/alter_table.sgml @@ -214,8 +214,17 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM <listitem> <para> These forms change whether a column is marked to allow null - values or to reject null values. You can only use <literal>SET - NOT NULL</literal> when the column contains no null values. + values or to reject null values. + </para> + + <para> + <literal>SET NOT NULL</literal> may only be applied to a column + providing none of the records in the table contain a + <literal>NULL</literal> value for the column. Ordinarily this is + checked during the <literal>ALTER TABLE</literal> by scanning the + entire table; however, if a valid <literal>CHECK</literal> constraint is + found which proves no <literal>NULL</literal> can exist, then the + table scan is skipped. </para> <para> |