SELECT
SQL - Language Statements
SELECT
Retrieve rows from a table or view
1998-04-15
SELECT [ALL|DISTINCT]
expression [AS name] [, ...]
[INTO [TABLE] intable]
[FROM table [alias] [, ...] ]
[WHERE condition]
[GROUP BY column [, ...] ]
[HAVING condition [, ...] ]
[UNION [ALL] select]
[ORDER BY column [ASC | DESC] [, ...] ]
1998-04-15
Inputs
expression
The name of a table's column or an expression.
name
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.
intable
If the INTO TABLE clause is specified, the result of the
query will be stored in another table with the indicated
name.
If intable does not exist, it will be created automatically.
The CREATE TABLE AS statement will also create a new table from a select query.
table
The name of an existing table referenced by FROM clause.
alias
An alternate name for the preceeding table.
Used for brevity or to eliminate ambiguity for joins within a single table.
condition
An expression leading to a boolean (true/false) result.
See the WHERE clause.
column
The name of a table's column.
select
A select statement with all features except the ORDER BY clause.
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Outputs
Rows
The complete set of rows resulting from the query specification.
count
The count of rows returned by the query.
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Description
SELECT will get all rows which satisfy the WHERE condition
or all rows of a table if WHERE is omitted.
The GROUP BY clause allows a user to divide a table
conceptually into groups. (See GROUP BY clause).
The HAVING clause specifies a grouped table derived by the
elimination of groups from the result of the previously
specified clause. (See HAVING clause).
The ORDER BY clause allows a user to specify that he/she
wishes the rows sorted according to the ASCending or
DESCending mode operator. (See ORDER BY clause)
The UNION clause specifies a table derived from a Cartesian
product union join. (See UNION clause).
You must have SELECT privilege to a table to read its values
(See GRANT/REVOKE statements).
1998-04-15
WHERE clause
The optional WHERE condition has the general form:
WHERE expr cond_op expr [log_op ...]
where cond_op can be one of: =, <, <=, >, >=, <>
or a conditional operator like ALL, ANY, IN, LIKE, et cetera
and log_op can be one of: AND, OR, NOT.
The comparison returns either TRUE or FALSE and all
instances will be discarded
if the expression evaluates to FALSE.
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GROUP BY clause
GROUP BY specifies a grouped table derived by the application
of the this clause:
GROUP BY column [, ...]
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HAVING clause
The optional HAVING condition has the general form:
HAVING cond_expr
where cond_expr is the same
as specified for the WHERE clause.
HAVING specifies a grouped table derived by the elimination
of groups from the result of the previously specified clause
that do not meet the cond_expr.
Each column referenced in cond_expr shall unambiguously
reference a grouping column.
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ORDER BY clause
ORDER BY column [ASC | DESC] [, ...]
column can be either a column
name or an ordinal number.
The ordinal numbers refers to the ordinal (left-to-right) position
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.:
SELECT title, date_prod + 1 AS newlen FROM films ORDER BY newlen;
The columns in the ORDER BY must appear in the SELECT clause.
Thus the following statement is illegal:
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.
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UNION clause
table_query UNION [ALL] table_query
[ORDER BY column [ASC | DESC] [, ...] ]
where
table_query
specifies any select expression without an ORDER BY clause.
The UNION operator specifies a table derived from a Cartesian product.
The two tables that represent the direct operands of the UNION must
have the same number of columns, and corresponding columns must be
of compatible data types.
By default, the result of UNION does not contain any duplicate rows
unless the ALL clause is specified.
Multiple UNION operators in the same SELECT statement are evaluated left to right.
Note that the ALL keyword is not global in nature, being applied only for the current pair of
table results.
Usage
--Join table films with their distributors:
--
SELECT f.title, f.did, d.name, f.date_prod, f.kind
FROM distributors d, films f
WHERE f.did = d.did;
title |did|name | date_prod|kind
-------------------------+---+----------------+----------+----------
The Third Man |101|British Lion |1949-12-23|Drama
The African Queen |101|British Lion |1951-08-11|Romantic
Une Femme est une Femme |102|Jean Luc Godard |1961-03-12|Romantic
Vertigo |103|Paramount |1958-11-14|Action
Becket |103|Paramount |1964-02-03|Drama
48 Hrs |103|Paramount |1982-10-22|Action
War and Peace |104|Mosfilm |1967-02-12|Drama
West Side Story |105|United Artists |1961-01-03|Musical
Bananas |105|United Artists |1971-07-13|Comedy
Yojimbo |106|Toho |1961-06-16|Drama
There's a Girl in my Soup|107|Columbia |1970-06-11|Comedy
Taxi Driver |107|Columbia |1975-05-15|Action
Absence of Malice |107|Columbia |1981-11-15|Action
Storia di una donna |108|Westward |1970-08-15|Romantic
The King and I |109|20th Century Fox|1956-08-11|Musical
Das Boot |110|Bavaria Atelier |1981-11-11|Drama
Bed Knobs and Broomsticks|111|Walt Disney | |Musical
--sum column "len" of all films group by "kind":
--
SELECT kind, SUM(len) AS total FROM films GROUP BY kind;
kind |total
----------+------
Action | 07:34
Comedy | 02:58
Drama | 14:28
Musical | 06:42
Romantic | 04:38
--sum column length of all films group by "kind"
--having total duration < 5 hours:
--
SELECT kind, SUM(len) AS total
FROM films
GROUP BY kind
HAVING SUM(len) < INTERVAL '5 hour';
kind |total
----------+------
Comedy | 02:58
Romantic | 04:38
--The following two examples are identicals:
--
SELECT * FROM distributors ORDER BY name;
SELECT * FROM distributors ORDER BY 2;
did|name
---+----------------
109|20th Century Fox
110|Bavaria Atelier
101|British Lion
107|Columbia
102|Jean Luc Godard
113|Luso films
104|Mosfilm
103|Paramount
106|Toho
105|United Artists
111|Walt Disney
112|Warner Bros.
108|Westward
--union of table distributors and table actors:
-- (only those that begin with letter W):
--
-- distributors: actors:
-- did|name id|name
-- ---+------------ --+--------------
-- 108|Westward 1|Woody Allen
-- 111|Walt Disney 2|Warren Beatty
-- 112|Warner Bros. 3|Walter Matthau
-- ... ...
--
--select only distinct rows (without ALL):
--
SELECT distributors.name
FROM distributors
WHERE distributors.name LIKE 'W%'
UNION
SELECT actors.name
FROM actors
WHERE actors.name LIKE 'W%';
name
--------------
Walt Disney
Walter Matthau
Warner Bros.
Warren Beatty
Westward
Woody Allen
Compatibility
1998-04-15
<Acronym>SQL92</Acronym>
1998-04-15
SELECT clause
In the SQL92 standard, the optional keyword "AS" is just noise and can be
omitted without affecting the meaning.
The Postgres parser requires this keyword when
renaming columns because the type extensibility features lead to 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.
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UNION clause
The SQL92 syntax for UNION allows an additional CORRESPONDING BY clause:
table_query UNION [ALL]
[CORRESPONDING [BY (column [,...])]]
table_query
The CORRESPONDING BY clause is not supported by Postgres.