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| author | Bruce Momjian <bruce@momjian.us> | 2020-05-21 19:49:30 -0400 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2020-05-21 19:49:30 -0400 |
| commit | c7c0db90c29c8cad31dc0aeb9131acac3d048dee (patch) | |
| tree | 4bf80b03ef26f52dabaadc671065dbaa3bd56d86 | |
| parent | 8de137017a158185b0dd022231aeb5ac2daede6b (diff) | |
| download | postgresql-c7c0db90c29c8cad31dc0aeb9131acac3d048dee.tar.gz postgresql-c7c0db90c29c8cad31dc0aeb9131acac3d048dee.zip | |
doc: Simplify mention of unique indexes for NULL control
Discussion: https://postgr.es/m/2304.1586532634@sss.pgh.pa.us
Backpatch-through: 9.5
| -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 6fbfdb9bda5..e2aa7091cc8 100644 --- a/doc/src/sgml/indices.sgml +++ b/doc/src/sgml/indices.sgml @@ -703,15 +703,6 @@ 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</>, it would prevent creation of rows whose <literal>col1</> values differ only in case, as well as rows whose <literal>col1</> values are actually identical. @@ -948,18 +939,11 @@ 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> |