diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index ed180ac91c1..674234d8e33 100644
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -1,5 +1,5 @@
@@ -30,9 +30,9 @@ SELECT [ ALL | DISTINCT [ ON ( expressioncolumn [, ...] ]
[ HAVING condition [, ...] ]
[ { UNION [ ALL ] | INTERSECT | EXCEPT } select ]
- [ ORDER BY column [ ASC | DESC ] [, ...] ]
- [ FOR UPDATE [ OF class_name... ] ]
- [ LIMIT { count | ALL } [ { OFFSET | , } count ] ]
+ [ ORDER BY column [ ASC | DESC | USING operator ] [, ...] ]
+ [ FOR UPDATE [ OF class_name [, ...] ] ]
+ LIMIT { count | ALL } [ { OFFSET | , } start ]
@@ -59,10 +59,10 @@ SELECT [ ALL | DISTINCT [ ON ( expression
Specifies another name for a column or an expression using
- the AS clause. name
- cannot be used in the WHERE
- condition. It can, however, be referenced in associated
- ORDER BY or GROUP BY clauses.
+ the AS clause. This name is primarily used to label the output
+ column. The name
+ cannot be used in the WHERE, GROUP BY, or HAVING clauses.
+ It can, however, be referenced in ORDER BY clauses.
@@ -245,18 +245,19 @@ SELECT [ ALL | DISTINCT [ ON ( expression
- The UNION clause allows the result to be the collection of rows
+ The UNION operator allows the result to be the collection of rows
returned by the queries involved.
(See .)
- The INTERSECT give you the rows that are common to both queries.
+ The INTERSECT operator gives you the rows that are common to both queries.
(See .)
- The EXCEPT give you the rows in the upper query not in the lower query.
+ The EXCEPT operator gives you the rows returned by the first query but
+ not the second query.
(See .)
@@ -266,8 +267,9 @@ SELECT [ ALL | DISTINCT [ ON ( expression
- The LIMIT clause allows control over which rows are
- returned by the query.
+ The LIMIT clause allows a subset of the rows produced by the query
+ to be returned to the user.
+ (See .)
@@ -395,15 +397,15 @@ ORDER BY column [ ASC | DESC ] [, .
of the column. This feature makes it possible to define an ordering
on the basis of a column that does not have a proper name.
This is never absolutely necessary because it is always possible
- assign a name
- to a calculated column using the AS clause, e.g.:
+ to assign a name to a calculated column using the AS clause, e.g.:
SELECT title, date_prod + 1 AS newlen FROM films ORDER BY newlen;
- From release 6.4 of PostgreSQL, the columns in the ORDER BY clause
- do not need to appear in the SELECT clause.
+ From release 6.4 of PostgreSQL, it is also possible to ORDER BY
+ arbitrary expressions, including fields that do not appear in the
+ SELECT result list.
Thus the following statement is now legal:
SELECT name FROM distributors ORDER BY code;
@@ -413,7 +415,9 @@ SELECT name FROM distributors ORDER BY code;
Optionally one may add the keyword DESC (descending)
or ASC (ascending) after each column name in the ORDER BY clause.
- If not specified, ASC is assumed by default.
+ If not specified, ASC is assumed by default. Alternatively, a
+ specific ordering operator name may be specified. ASC is equivalent
+ to USING '<' and DESC is equivalent to USING '>'.
@@ -436,10 +440,10 @@ SELECT name FROM distributors ORDER BY code;
- The UNION clause allows the result to be the collection of rows
- returned by the queries involved. (See UNION clause).
- The two tables that represent the direct operands of the UNION must
- have the same number of columns, and corresponding columns must be
+ The UNION operator allows the result to be the collection of rows
+ returned by the queries involved.
+ The two SELECTs that represent the direct operands of the UNION must
+ produce the same number of columns, and corresponding columns must be
of compatible data types.
@@ -476,16 +480,15 @@ SELECT name FROM distributors ORDER BY code;
- The INTERSECT clause allows the result to be all rows that are
- common to the involved queries.
- The two tables that represent the direct operands of the INTERSECT must
- have the same number of columns, and corresponding columns must be
+ The INTERSECT operator gives you the rows that are common to both queries.
+ The two SELECTs that represent the direct operands of the INTERSECT must
+ produce the same number of columns, and corresponding columns must be
of compatible data types.
Multiple INTERSECT operators in the same SELECT statement are
- evaluated left to right.
+ evaluated left to right, unless parentheses dictate otherwise.
@@ -508,16 +511,65 @@ SELECT name FROM distributors ORDER BY code;
- The EXCEPT clause allows the result to be rows from the upper query
- that are not in the lower query. (See EXCEPT clause).
- The two tables that represent the direct operands of the EXCEPT must
- have the same number of columns, and corresponding columns must be
+ The EXCEPT operator gives you the rows returned by the first query but
+ not the second query.
+ The two SELECTs that represent the direct operands of the EXCEPT must
+ produce the same number of columns, and corresponding columns must be
of compatible data types.
Multiple EXCEPT operators in the same SELECT statement are
- evaluated left to right.
+ evaluated left to right, unless parentheses dictate otherwise.
+
+
+
+
+
+ 2000-02-20
+
+
+ LIMIT Clause
+
+
+
+ LIMIT { count | ALL } [ { OFFSET | , } start ]
+ OFFSET start
+
+
+ where
+ count specifies the
+ maximum number of rows to return, and
+ start specifies the
+ number of rows to skip before starting to return rows.
+
+
+
+ LIMIT allows you to retrieve just a portion of the rows that are generated
+ by the rest of the query. If a limit count is given, no more than that
+ many rows will be returned. If an offset is given, that many rows will
+ be skipped before starting to return rows.
+
+
+
+ When using LIMIT, it is a good idea to use an ORDER BY clause that
+ constrains the result rows into a unique order. Otherwise you will get
+ an unpredictable subset of the query's rows --- you may be asking for
+ the tenth through twentieth rows, but tenth through twentieth in what
+ ordering? You don't know what ordering, unless you specified ORDER BY.
+
+
+
+ As of Postgres 7.0, the
+ query optimizer takes LIMIT into account when generating a query plan,
+ so you are very likely to get different plans (yielding different row
+ orders) depending on what you give for LIMIT and OFFSET. Thus, using
+ different LIMIT/OFFSET values to select different subsets of a query
+ result will give inconsistent results unless
+ you enforce a predictable result ordering with ORDER BY. This is not
+ a bug; it is an inherent consequence of the fact that SQL does not
+ promise to deliver the results of a query in any particular order
+ unless ORDER BY is used to constrain the order.
@@ -624,7 +676,7 @@ SELECT * FROM distributors ORDER BY 2;
This example shows how to obtain the union of the tables
distributors and
actors, restricting the results to those that begin
- with letter W in each table. Only distinct rows are to be used, so the
+ with letter W in each table. Only distinct rows are wanted, so the
ALL keyword is omitted:
@@ -709,16 +761,9 @@ SELECT distributors.* WHERE name = 'Westwood';
parsing ambiguities
in this context.
-
- In the SQL92 standard, the new column name
- specified in an
- "AS" clause may be referenced in GROUP BY and HAVING clauses.
- This is not currently
- allowed in Postgres.
-
-
The DISTINCT ON phrase is not part of SQL92.
+ Nor are LIMIT and OFFSET.
diff --git a/doc/src/sgml/ref/select_into.sgml b/doc/src/sgml/ref/select_into.sgml
index 6617d07e5a6..277b2058740 100644
--- a/doc/src/sgml/ref/select_into.sgml
+++ b/doc/src/sgml/ref/select_into.sgml
@@ -1,5 +1,5 @@
@@ -22,16 +22,17 @@ Postgres documentation
1999-07-20
-SELECT [ ALL | DISTINCT ] expression [ AS name ] [, ...]
- INTO [TEMP] [ TABLE ] new_table ]
- [ FROM table [alias] [, ...] ]
+SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
+ expression [ AS name ] [, ...]
+ [ INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table ]
+ [ FROM table [ alias ] [, ...] ]
[ WHERE condition ]
[ GROUP BY column [, ...] ]
[ HAVING condition [, ...] ]
- [ { UNION [ALL] | INTERSECT | EXCEPT } select]
- [ ORDER BY column [ ASC | DESC ] [, ...] ]
- [ FOR UPDATE [OF class_name...]]
- [ LIMIT count [OFFSET|, count]]
+ [ { UNION [ ALL ] | INTERSECT | EXCEPT } select ]
+ [ ORDER BY column [ ASC | DESC | USING operator ] [, ...] ]
+ [ FOR UPDATE [ OF class_name [, ...] ] ]
+ LIMIT { count | ALL } [ { OFFSET | , } start ]