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| author | Tom Lane <tgl@sss.pgh.pa.us> | 1999-05-20 03:22:01 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 1999-05-20 03:22:01 +0000 |
| commit | c3a4d8ed54468a7778797b1075bcc443cd45be4b (patch) | |
| tree | a90ed54382c2b90707f7da85d2021f205a2566c4 /src | |
| parent | c9f8ab6fba29e1e09b6cf79881786bd0779b6e2b (diff) | |
| download | postgresql-c3a4d8ed54468a7778797b1075bcc443cd45be4b.tar.gz postgresql-c3a4d8ed54468a7778797b1075bcc443cd45be4b.zip | |
Very minor improvements in CREATE OPERATOR docs.
Diffstat (limited to 'src')
| -rw-r--r-- | src/man/create_operator.l | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/src/man/create_operator.l b/src/man/create_operator.l index 7fca24eb083..c1167ca3b25 100644 --- a/src/man/create_operator.l +++ b/src/man/create_operator.l @@ -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 |