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