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| -rw-r--r-- | doc/src/sgml/indices.sgml | 22 |
1 files changed, 3 insertions, 19 deletions
diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml index 86539a781c5..56fd0a3d3d3 100644 --- a/doc/src/sgml/indices.sgml +++ b/doc/src/sgml/indices.sgml @@ -706,15 +706,6 @@ CREATE INDEX test1_lower_col1_idx ON test1 (lower(col1)); </para> <para> - Expression indexes also allow control over the scope of unique indexes. - For example, this unique index prevents duplicate integer values from - being stored in a <type>double precision</type>-typed column: -<programlisting> -CREATE UNIQUE INDEX test1_uniq_int ON tests ((floor(double_col))) -</programlisting> - </para> - - <para> If we were to declare this index <literal>UNIQUE</literal>, it would prevent creation of rows whose <literal>col1</literal> values differ only in case, as well as rows whose <literal>col1</literal> values are actually identical. @@ -953,18 +944,11 @@ CREATE UNIQUE INDEX tests_success_constraint ON tests (subject, target) WHERE success; </programlisting> This is a particularly efficient approach when there are few - successful tests and many unsuccessful ones. + successful tests and many unsuccessful ones. It is also possible to + allow only one null in a column by creating a unique partial index + with an <literal>IS NULL</literal> restriction. </para> - <para> - This index allows only one null in the indexed column by using a - partial index clause to process only null column values, and using - an expression index clause to index <literal>true</literal> instead - of <literal>null</literal>: -<programlisting> -CREATE UNIQUE INDEX tests_target_one_null ON tests ((target IS NULL)) WHERE target IS NULL; -</programlisting> - </para> </example> <para> |