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Add note clarifying that indexes that support ordered scans had better

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allow clauseless scans.
This commit is contained in:
Tom Lane 2005-04-20 22:19:58 +00:00
parent eb4f58ad40
commit 1c155c8dfb
1 changed files with 3 additions and 2 deletions
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doc/src/sgml/indexam.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.3 2005/03/27 23:52:51 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.4 2005/04/20 22:19:58 tgl Exp $
-->
<chapter id="indexam">
@ -109,7 +109,8 @@ $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.3 2005/03/27 23:52:51 tgl Exp $
such a scan should include null rows. In practice this means that
indexes that support ordered scans (have <structfield>amorderstrategy</>
nonzero) must index nulls, since the planner might decide to use such a
scan as a substitute for sorting. Another restriction is that an index
scan as a substitute for sorting. Such indexes must also be willing to
run a scan with no scan keys at all. Another restriction is that an index
access method that supports multiple index columns <emphasis>must</>
support indexing null values in columns after the first, because the planner
will assume the index can be used for queries on just the first