diff options
Diffstat (limited to 'doc/src/sgml/ref/create_operator.sgml')
| -rw-r--r-- | doc/src/sgml/ref/create_operator.sgml | 17 |
1 files changed, 9 insertions, 8 deletions
diff --git a/doc/src/sgml/ref/create_operator.sgml b/doc/src/sgml/ref/create_operator.sgml index eda81ffa895..1e745a45f7c 100644 --- a/doc/src/sgml/ref/create_operator.sgml +++ b/doc/src/sgml/ref/create_operator.sgml @@ -227,11 +227,11 @@ Operator that sorts the right-hand data type of this operator. (either one or two). </para> <para> - The commutator operator is present so that - <productname>Postgres</productname> can + The commutator operator should be identified if one exists, + so that <productname>Postgres</productname> can reverse the order of the operands if it wishes. For example, the operator area-less-than, <<<, - would have a commutator + would probably have a commutator operator, area-greater-than, >>>. Hence, the query optimizer could freely convert: <programlisting> @@ -243,14 +243,15 @@ Operator that sorts the right-hand data type of this operator. </para> <para> This allows the execution code to always use the latter - representation and simplifies the query optimizer some - what. + representation and simplifies the query optimizer somewhat. </para> <para> + Similarly, if there is a negator operator then it should be + identified. Suppose that an operator, area-equal, ===, exists, as well as an area not equal, !==. - The negator operator allows the query optimizer to convert + The negator link allows the query optimizer to simplify <programlisting> NOT MYBOXES.description === "0,0,1,1"::box </programlisting> @@ -325,8 +326,8 @@ Operator that sorts the right-hand data type of this operator. satisfy the clause. The function <replaceable class="parameter">res_proc</replaceable> must be a registered function (meaning it is already defined using - define function(l)) which accepts one argument of the correct - data type and returns a floating point number. The + CREATE FUNCTION) which accepts arguments of the correct + data types and returns a floating point number. The query optimizer simply calls this function, passing the parameter "0,0,1,1" and multiplies the result by the relation size to get the desired expected number of instances. |