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Support ORDER BY ... NULLS FIRST/LAST, and add ASC/DESC/NULLS FIRST/NULLS LAST

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per-column options for btree indexes.  The planner's support for this is still
pretty rudimentary; it does not yet know how to plan mergejoins with
nondefault ordering options.  The documentation is pretty rudimentary, too.
I'll work on improving that stuff later.

Note incompatible change from prior behavior: ORDER BY ... USING will now be
rejected if the operator is not a less-than or greater-than member of some
btree opclass.  This prevents less-than-sane behavior if an operator that
doesn't actually define a proper sort ordering is selected.
This commit is contained in:
Tom Lane
2007-01-09 02:14:16 +00:00
parent 3a32ba2f3f
commit 4431758229
65 changed files with 1476 additions and 593 deletions
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64
doc/src/sgml/ref/create_index.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.58 2006/09/16 00:30:17 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.59 2007/01/09 02:14:10 tgl Exp $
PostgreSQL documentation
-->
@@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] <replaceable class="parameter">name</replaceable> ON <replaceable class="parameter">table</replaceable> [ USING <replaceable class="parameter">method</replaceable> ]
( { <replaceable class="parameter">column</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ <replaceable class="parameter">opclass</replaceable> ] [, ...] )
( { <replaceable class="parameter">column</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ <replaceable class="parameter">opclass</replaceable> ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] ) ]
[ TABLESPACE <replaceable class="parameter">tablespace</replaceable> ]
[ WHERE <replaceable class="parameter">predicate</replaceable> ]
@@ -187,6 +187,44 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] <replaceable class="parameter">name</re
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ASC</></term>
<listitem>
<para>
Specifies ascending sort order (which is the default).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DESC</></term>
<listitem>
<para>
Specifies descending sort order.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>NULLS FIRST</></term>
<listitem>
<para>
Specifies that nulls sort before non-nulls. This is the default
when <literal>DESC</> is specified.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>NULLS LAST</></term>
<listitem>
<para>
Specifies that nulls sort after non-nulls. This is the default
when <literal>DESC</> is not specified.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">storage_parameter</replaceable></term>
<listitem>
@@ -363,6 +401,21 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] <replaceable class="parameter">name</re
linkend="xindex">.
</para>
<para>
For index methods that support ordered scans (currently, only B-tree),
the optional clauses <literal>ASC</>, <literal>DESC</>, <literal>NULLS
FIRST</>, and/or <literal>NULLS LAST</> can be specified to reverse
the normal sort direction of the index. Since an ordered index can be
scanned either forward or backward, it is not normally useful to create a
single-column <literal>DESC</> index &mdash; that sort ordering is already
available with a regular index. The value of these options is that
multicolumn indexes can be created that match the sort ordering requested
by a mixed-ordering query, such as <literal>SELECT ... ORDER BY x ASC, y
DESC</>. The <literal>NULLS</> options are useful if you need to support
<quote>nulls sort low</> behavior, rather than the default <quote>nulls
sort high</>, in queries that depend on indexes to avoid sorting steps.
</para>
<para>
Use <xref linkend="sql-dropindex" endterm="sql-dropindex-title">
to remove an index.
@@ -403,6 +456,13 @@ CREATE INDEX lower_title_idx ON films ((lower(title)));
</programlisting>
</para>
<para>
To create an index with non-default sort ordering of nulls:
<programlisting>
CREATE INDEX title_idx_nulls_low ON films (title NULLS FIRST);
</programlisting>
</para>
<para>
To create an index with non-default fill factor:
<programlisting>

23
doc/src/sgml/ref/select.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.94 2006/12/01 20:49:53 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.95 2007/01/09 02:14:10 tgl Exp $
PostgreSQL documentation
-->
@@ -27,7 +27,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
[ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...] ]
[ HAVING <replaceable class="parameter">condition</replaceable> [, ...] ]
[ { UNION | INTERSECT | EXCEPT } [ ALL ] <replaceable class="parameter">select</replaceable> ]
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [, ...] ]
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ LIMIT { <replaceable class="parameter">count</replaceable> | ALL } ]
[ OFFSET <replaceable class="parameter">start</replaceable> ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ] [...] ]
@@ -642,7 +642,7 @@ HAVING <replaceable class="parameter">condition</replaceable>
<para>
The optional <literal>ORDER BY</literal> clause has this general form:
<synopsis>
ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [, ...]
ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...]
</synopsis>
<replaceable class="parameter">expression</replaceable> can be the
name or ordinal number of an output column
@@ -652,8 +652,8 @@ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC |
<para>
The <literal>ORDER BY</literal> clause causes the result rows to
be sorted according to the specified expressions. If two rows are
equal according to the leftmost expression, the are compared
be sorted according to the specified expression(s). If two rows are
equal according to the leftmost expression, they are compared
according to the next expression and so on. If they are equal
according to all specified expressions, they are returned in
an implementation-dependent order.
@@ -697,6 +697,8 @@ SELECT name FROM distributors ORDER BY code;
<literal>ORDER BY</> clause. If not specified, <literal>ASC</> is
assumed by default. Alternatively, a specific ordering operator
name may be specified in the <literal>USING</> clause.
An ordering operator must be a less-than or greater-than
member of some btree operator family.
<literal>ASC</> is usually equivalent to <literal>USING &lt;</> and
<literal>DESC</> is usually equivalent to <literal>USING &gt;</>.
(But the creator of a user-defined data type can define exactly what the
@@ -705,9 +707,14 @@ SELECT name FROM distributors ORDER BY code;
</para>
<para>
The null value sorts higher than any other value. In other words,
with ascending sort order, null values sort at the end, and with
descending sort order, null values sort at the beginning.
If <literal>NULLS LAST</> is specified, null values sort after all
non-null values; if <literal>NULLS FIRST</> is specified, null values
sort before all non-null values. If neither is specified, the default
behavior is <literal>NULLS LAST</> when <literal>ASC</> is specified
or implied, and <literal>NULLS FIRST</> when <literal>DESC</> is specified
(thus, the default is to act as though nulls are larger than non-nulls).
When <literal>USING</> is specified, the default nulls ordering depends
on whether the operator is a less-than or greater-than operator.
</para>
<para>

4
doc/src/sgml/ref/select_into.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select_into.sgml,v 1.38 2006/09/16 00:30:20 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select_into.sgml,v 1.39 2007/01/09 02:14:10 tgl Exp $
PostgreSQL documentation
-->
@@ -28,7 +28,7 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="PARAMETER">expression</replac
[ GROUP BY <replaceable class="PARAMETER">expression</replaceable> [, ...] ]
[ HAVING <replaceable class="PARAMETER">condition</replaceable> [, ...] ]
[ { UNION | INTERSECT | EXCEPT } [ ALL ] <replaceable class="PARAMETER">select</replaceable> ]
[ ORDER BY <replaceable class="PARAMETER">expression</replaceable> [ ASC | DESC | USING <replaceable class="PARAMETER">operator</replaceable> ] [, ...] ]
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ LIMIT { <replaceable class="PARAMETER">count</replaceable> | ALL } ]
[ OFFSET <replaceable class="PARAMETER">start</replaceable> ]
[ FOR { UPDATE | SHARE } [ OF <replaceable class="parameter">table_name</replaceable> [, ...] ] [ NOWAIT ] [...] ]