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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).
</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.