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Commitc3a4d8e

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Very minor improvements in CREATE OPERATOR docs.
1 parentc9f8ab6 commitc3a4d8e

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‎doc/src/sgml/ref/create_operator.sgml

Lines changed: 9 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -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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Thecommutatoroperator is present so that
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<productname>Postgres</productname> can
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The commutator operatorshould 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, &lt;&lt;&lt;,
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would have a commutator
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wouldprobablyhave a commutator
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operator, area-greater-than, &gt;&gt;&gt;.
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Hence, the query optimizer could freely convert:
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<programlisting>
@@ -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 negatoroperator allows the query optimizer toconvert
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The negatorlink allows the query optimizer tosimplify
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<programlisting>
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NOT MYBOXES.description === "0,0,1,1"::box
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</programlisting>
@@ -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 acceptsone argument of the correct
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datatype and returns a floating point number. The
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CREATE FUNCTION) which acceptsarguments of the correct
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datatypes 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.

‎src/man/create_operator.l

Lines changed: 8 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,6 @@
11
.\" This is -*-nroff-*-
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.\" XXX standard disclaimer belongs here....
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.\" $Header: /cvsroot/pgsql/src/man/Attic/create_operator.l,v 1.8 1999/04/15 00:09:00 tgl Exp $
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.\" $Header: /cvsroot/pgsql/src/man/Attic/create_operator.l,v 1.9 1999/05/20 03:21:02 tgl Exp $
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.TH "CREATE OPERATOR" SQL 11/05/95 PostgreSQL PostgreSQL
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.SH NAME
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create operator - define a new user operator
@@ -88,9 +88,10 @@ and must have one or two arguments.
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.\" .(l
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.\" MYBOXES2.description A (\*(lq0,0,1,1\*(rq A MYBOXES.description).
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.\" .)l
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The commutator operator is present so that Postgres can reverse the order
92-
of the operands if it wishes. For example, the operator
93-
area-less-than, >>>, would have a commutator operator,
91+
The commutator operator should be identified if one exists,
92+
so that Postgres can reverse the order of the operands if it wishes.
93+
For example, the operator
94+
area-less-than, >>>, would probably have a commutator operator,
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area-greater-than, <<<. Hence, the query optimizer
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could freely convert:
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.nf
@@ -109,9 +110,10 @@ MYBOXES.description <<< "0,0,1,1"::box
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This allows the execution code to always use the latter representation
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and simplifies the query optimizer somewhat.
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.PP
113+
Similarly, if there is a negator operator then it should be identified.
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Suppose that an operator, area-equal, ===,
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exists, as well as an area not equal, !==.
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The negatoroperator allows the query optimizer toconvert
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The negatorlink allows the query optimizer tosimplify
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.nf
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.ce1
@@ -182,7 +184,7 @@ fraction of the instances in MYBOXES that satisfy the clause. The
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function res_proc must be a registered function (meaning it is already
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defined using
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.IR create_function(l))
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which acceptsone argumentof the correct datatype and returns a
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which acceptsargumentsof the correct datatypes and returns a
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floating point number. The query optimizer simply calls this
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function, passing the parameter "0,0,1,1"
188190
and multiplies the result by the relation size to get the desired

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