Text Size: Normal / Large

Home → Documentation → Manuals → PostgreSQL 8.1

PostgreSQL 8.1.8 Documentation
Prev	Fast Backward	Chapter 9. Functions and Operators	Fast Forward	Next

9.15. Aggregate Functions

Aggregate functions compute a single result value from a set of input values. Table 9-37 shows the built-in aggregate functions. The special syntax considerations for aggregate functions are explained in Section 4.2.7. Consult Section 2.7 for additional introductory information.

Table 9-37. Aggregate Functions

Function	Argument Type	Return Type	Description
`avg(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`, or `interval`	`numeric` for any integer type argument, `double precision` for a floating-point argument, otherwise the same as the argument data type	the average (arithmetic mean) of all input values
`bit_and(expression)`	`smallint`, `int`, `bigint`, or `bit`	same as argument data type	the bitwise AND of all non-null input values, or null if none
`bit_or(expression)`	`smallint`, `int`, `bigint`, or `bit`	same as argument data type	the bitwise OR of all non-null input values, or null if none
`bool_and(expression)`	`bool`	`bool`	true if all input values are true, otherwise false
`bool_or(expression)`	`bool`	`bool`	true if at least one input value is true, otherwise false
`count(*)`		`bigint`	number of input values
`count(expression)`	any	`bigint`	number of input values for which the value of `expression` is not null
`every(expression)`	`bool`	`bool`	equivalent to `bool_and`
`max(expression)`	any array, numeric, string, or date/time type	same as argument type	maximum value of `expression` across all input values
`min(expression)`	any array, numeric, string, or date/time type	same as argument type	minimum value of `expression` across all input values
`stddev(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, or `numeric`	`double precision` for floating-point arguments, otherwise `numeric`	sample standard deviation of the input values
`sum(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`, or `interval`	`bigint` for `smallint` or `int` arguments, `numeric` for `bigint` arguments, `double precision` for floating-point arguments, otherwise the same as the argument data type	sum of `expression` across all input values
`variance`(`expression`)	`smallint`, `int`, `bigint`, `real`, `double precision`, or `numeric`	`double precision` for floating-point arguments, otherwise `numeric`	sample variance of the input values (square of the sample standard deviation)

It should be noted that except for count, these functions return a null value when no rows are selected. In particular, sum of no rows returns null, not zero as one might expect. The coalesce function may be used to substitute zero for null when necessary.

Note: Boolean aggregates bool_and and bool_or correspond to standard SQL aggregates every and any or some. As for any and some, it seems that there is an ambiguity built into the standard syntax:
SELECT b1 = ANY((SELECT b2 FROM t2 ...)) FROM t1 ...;
Here ANY can be considered both as leading to a subquery or as an aggregate if the select expression returns 1 row. Thus the standard name cannot be given to these aggregates.

Note: Users accustomed to working with other SQL database management systems may be surprised by the performance of the count aggregate when it is applied to the entire table. A query like:
SELECT count(*) FROM sometable;
will be executed by PostgreSQL using a sequential scan of the entire table.

Prev	Home	Next
Array Functions and Operators	Up	Subquery Expressions

User Comments

No comments could be found for this page.

Add Comment

Please use this form to add your own comments regarding your experience with particular features of PostgreSQL, clarifications of the documentation, or hints for other users. Please note, this is not a support forum, and your IP address will be logged. If you have a question or need help, please see the faq, try a mailing list, or join us on IRC. Note that submissions containing URLs or other keywords commonly found in 'spam' comments may be silently discarded. Please contact the webmaster if you think this is happening to you in error.

In order to submit a comment, you must have a community account.

* denotes required field