database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-08-30 06:01:21 +03:00
Code Activity

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

Browse Source 
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
Download Patch File Download Diff File Expand all files Collapse all files

15
doc/src/sgml/queries.sgml
View File

@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/queries.sgml,v 1.39 2006/10/24 02:24:27 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/queries.sgml,v 1.40 2007/01/09 02:14:10 tgl Exp $ -->
<chapter id="queries">
<title>Queries</title>
@@ -1224,7 +1224,8 @@ SELECT DISTINCT ON (<replaceable>expression</replaceable> <optional>, <replaceab
<synopsis>
SELECT <replaceable>select_list</replaceable>
FROM <replaceable>table_expression</replaceable>
ORDER BY <replaceable>sort_expression1</replaceable> <optional>ASC | DESC</optional> <optional>, <replaceable>sort_expression2</replaceable> <optional>ASC | DESC</optional> ...</optional>
ORDER BY <replaceable>sort_expression1</replaceable> <optional>ASC | DESC</optional> <optional>NULLS { FIRST | LAST }</optional>
<optional>, <replaceable>sort_expression2</replaceable> <optional>ASC | DESC</optional> <optional>NULLS { FIRST | LAST }</optional> ...</optional>
</synopsis>
The sort expression(s) can be any expression that would be valid in the
query's select list. An example is
@@ -1253,6 +1254,14 @@ SELECT a, b FROM table1 ORDER BY a + b, c;
</footnote>
</para>
<para>
The <literal>NULLS FIRST</> and <literal>NULLS LAST</> options can be
used to determine whether nulls appear before or after non-null values
in the sort ordering. By default, null values sort as if larger than any
non-null value; that is, <literal>NULLS FIRST</> is the default for
<literal>DESC</> order, and <literal>NULLS LAST</> otherwise.
</para>
<para>
For backwards compatibility with the SQL92 version of the standard,
a <replaceable>sort_expression</> can instead be the name or number
@@ -1301,7 +1310,7 @@ SELECT a + b AS sum, c FROM table1 ORDER BY sum + c; -- wrong
<synopsis>
SELECT <replaceable>select_list</replaceable>
FROM <replaceable>table_expression</replaceable>
<optional> ORDER BY <replaceable>sort_expression1</replaceable> <optional>ASC | DESC</optional> <optional>, <replaceable>sort_expression2</replaceable> <optional>ASC | DESC</optional> ...</optional> </optional>
<optional> ORDER BY ... </optional>
<optional> LIMIT { <replaceable>number</replaceable> | ALL } </optional> <optional> OFFSET <replaceable>number</replaceable> </optional>
</synopsis>
</para>