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Very minor improvements in CREATE OPERATOR docs.

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
View File

@ -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, &lt;&lt;&lt;,
would have a commutator
would probably have a commutator
operator, area-greater-than, &gt;&gt;&gt;.
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.

14
src/man/create_operator.l
View File

@ -1,6 +1,6 @@
.\" This is -*-nroff-*-
.\" 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
.SH NAME
create operator - define a new user operator
@ -88,9 +88,10 @@ and must have one or two arguments.
.\" .(l
.\" MYBOXES2.description A (\*(lq0,0,1,1\*(rq A MYBOXES.description).
.\" .)l
The commutator operator is present so that Postgres can reverse the order
of the operands if it wishes. For example, the operator
area-less-than, >>>, would have a commutator operator,
The commutator operator should be identified if one exists,
so that Postgres can reverse the order of the operands if it wishes.
For example, the operator
area-less-than, >>>, would probably have a commutator operator,
area-greater-than, <<<. Hence, the query optimizer
could freely convert:
.nf
@ -109,9 +110,10 @@ MYBOXES.description <<< "0,0,1,1"::box
This allows the execution code to always use the latter representation
and simplifies the query optimizer somewhat.
.PP
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
.nf
.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
defined using
.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
function, passing the parameter "0,0,1,1"
and multiplies the result by the relation size to get the desired