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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"> <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 such a scan should include null rows. In practice this means that
indexes that support ordered scans (have <structfield>amorderstrategy</> indexes that support ordered scans (have <structfield>amorderstrategy</>
nonzero) must index nulls, since the planner might decide to use such a 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</> access method that supports multiple index columns <emphasis>must</>
support indexing null values in columns after the first, because the planner 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 will assume the index can be used for queries on just the first