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Very minor improvements in CREATE OPERATOR docs.

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This commit is contained in:
Tom Lane 1999-05-20 03:22:01 +00:00
parent c9f8ab6fba
commit c3a4d8ed54
2 changed files with 17 additions and 14 deletions
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17
doc/src/sgml/ref/create_operator.sgml
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@ -227,11 +227,11 @@ Operator that sorts the right-hand data type of this operator.
(either one or two). (either one or two).
</para> </para>
<para> <para>
The commutator operator is present so that The commutator operator should be identified if one exists,
<productname>Postgres</productname> can so that <productname>Postgres</productname> can
reverse the order of the operands if it wishes. reverse the order of the operands if it wishes.
For example, the operator area-less-than, &lt;&lt;&lt;, For example, the operator area-less-than, &lt;&lt;&lt;,
would have a commutator would probably have a commutator
operator, area-greater-than, &gt;&gt;&gt;. operator, area-greater-than, &gt;&gt;&gt;.
Hence, the query optimizer could freely convert: Hence, the query optimizer could freely convert:
<programlisting> <programlisting>
@ -243,14 +243,15 @@ Operator that sorts the right-hand data type of this operator.
</para> </para>
<para> <para>
This allows the execution code to always use the latter This allows the execution code to always use the latter
representation and simplifies the query optimizer some representation and simplifies the query optimizer somewhat.
what.
</para> </para>
<para> <para>
Similarly, if there is a negator operator then it should be
identified.
Suppose that an Suppose that an
operator, area-equal, ===, exists, as well as an area not operator, area-equal, ===, exists, as well as an area not
equal, !==. equal, !==.
The negator operator allows the query optimizer to convert The negator link allows the query optimizer to simplify
<programlisting> <programlisting>
NOT MYBOXES.description === "0,0,1,1"::box NOT MYBOXES.description === "0,0,1,1"::box
</programlisting> </programlisting>
@ -325,8 +326,8 @@ Operator that sorts the right-hand data type of this operator.
satisfy the clause. The function satisfy the clause. The function
<replaceable class="parameter">res_proc</replaceable> <replaceable class="parameter">res_proc</replaceable>
must be a registered function (meaning it is already defined using must be a registered function (meaning it is already defined using
define function(l)) which accepts one argument of the correct CREATE FUNCTION) which accepts arguments of the correct
data type and returns a floating point number. The data types and returns a floating point number. The
query optimizer simply calls this function, passing the query optimizer simply calls this function, passing the
parameter "0,0,1,1" and multiplies the result by the relation parameter "0,0,1,1" and multiplies the result by the relation
size to get the desired expected number of instances. size to get the desired expected number of instances.

14
src/man/create_operator.l
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@ -1,6 +1,6 @@
.\" This is -*-nroff-*- .\" This is -*-nroff-*-
.\" XXX standard disclaimer belongs here.... .\" XXX standard disclaimer belongs here....
.\" $Header: /cvsroot/pgsql/src/man/Attic/create_operator.l,v 1.8 1999/04/15 00:09:00 tgl Exp $ .\" $Header: /cvsroot/pgsql/src/man/Attic/create_operator.l,v 1.9 1999/05/20 03:21:02 tgl Exp $
.TH "CREATE OPERATOR" SQL 11/05/95 PostgreSQL PostgreSQL .TH "CREATE OPERATOR" SQL 11/05/95 PostgreSQL PostgreSQL
.SH NAME .SH NAME
create operator - define a new user operator create operator - define a new user operator
@ -88,9 +88,10 @@ and must have one or two arguments.
.\" .(l .\" .(l
.\" MYBOXES2.description A (\*(lq0,0,1,1\*(rq A MYBOXES.description). .\" MYBOXES2.description A (\*(lq0,0,1,1\*(rq A MYBOXES.description).
.\" .)l .\" .)l
The commutator operator is present so that Postgres can reverse the order The commutator operator should be identified if one exists,
of the operands if it wishes. For example, the operator so that Postgres can reverse the order of the operands if it wishes.
area-less-than, >>>, would have a commutator operator, For example, the operator
area-less-than, >>>, would probably have a commutator operator,
area-greater-than, <<<. Hence, the query optimizer area-greater-than, <<<. Hence, the query optimizer
could freely convert: could freely convert:
.nf .nf
@ -109,9 +110,10 @@ MYBOXES.description <<< "0,0,1,1"::box
This allows the execution code to always use the latter representation This allows the execution code to always use the latter representation
and simplifies the query optimizer somewhat. and simplifies the query optimizer somewhat.
.PP .PP
Similarly, if there is a negator operator then it should be identified.
Suppose that an operator, area-equal, ===, Suppose that an operator, area-equal, ===,
exists, as well as an area not 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
.nf .nf
.ce 1 .ce 1
@ -182,7 +184,7 @@ fraction of the instances in MYBOXES that satisfy the clause. The
function res_proc must be a registered function (meaning it is already function res_proc must be a registered function (meaning it is already
defined using defined using
.IR create_function(l)) .IR create_function(l))
which accepts one argument of the correct data type and returns a which accepts arguments of the correct data types and returns a
floating point number. The query optimizer simply calls this floating point number. The query optimizer simply calls this
function, passing the parameter "0,0,1,1" function, passing the parameter "0,0,1,1"
and multiplies the result by the relation size to get the desired and multiplies the result by the relation size to get the desired