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Modify partial-index-predicate applicability tester to test whether

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clauses are equal(), before trying to match them up using btree opclass
inference rules.  This allows it to recognize many simple cases involving
non-btree operations, for example 'x IS NULL'.  Clean up code a little.
This commit is contained in:
Tom Lane
2001-08-06 18:09:45 +00:00
parent 7d6fbe15a2
commit 246793469e
3 changed files with 98 additions and 82 deletions
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27
doc/src/sgml/ref/create_index.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.20 2001/07/16 05:06:57 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.21 2001/08/06 18:09:45 tgl Exp $
Postgres documentation
-->
@ -256,21 +256,26 @@ ERROR: Cannot create index: 'index_name' already exists.
billed and unbilled orders where the unbilled orders take up a small
fraction of the total table and yet that is an often used section, you
can improve performance by creating an index on just that portion.
Another possible application is to use <command>WHERE</command> with
<command>UNIQUE</command> to enforce uniqueness over a subset of a
table.
</para>
<para>
The expression used in the <command>WHERE</command> clause may refer
only to columns of the underlying table (but it can use all columns,
not only the one(s) being indexed). Currently, the
<productname>PostgreSQL</productname> planner can only devise query
plans that make use of a partial index when the predicate is built from
<command>AND</command> and <command>OR</command> combinations of
elements of the form
<firstterm>column</firstterm>
<firstterm>operator</firstterm>
<firstterm>constant</firstterm>.
However, more general predicates may still be useful in conjunction
with UNIQUE indexes, to enforce uniqueness over a subset of a table.
not only the one(s) being indexed). Presently, sub-SELECTs and
aggregate expressions are also forbidden in <command>WHERE</command>.
</para>
<para>
All functions and operators used in an index definition must be
<firstterm>cachable</>, that is, their results must depend only on
their input arguments and never on any outside influence (such as
the contents of another table or the current time). This restriction
ensures that the behavior of the index is well-defined. To use a
user-defined function in an index, remember to mark the function cachable
when you create it.
</para>
<para>