8.10. Aggregate Functions

Aggregate functions operate on groups of records, rather than on individual records or variables. They are often used in combination with a GROUP BY clause.

8.10.1. AVG()

Available in

DSQL, ESQL, PSQL

Syntax

AVG ([ALL | DISTINCT] <expr>)

Result type

A numeric data type, the same as the data type of the argument.

Description

AVG returns the average argument value in the group. NULL is ignored.

• Parameter ALL (the default) applies the aggregate function to all values.

• Parameter DISTINCT directs the AVG function to consider only one instance of each unique value, no matter how many times this value occurs.

• If the set of retrieved records is empty or contains only NULL, the result will be NULL.

Example

SELECT
  dept_no,
  AVG(salary)
FROM employee
GROUP BY dept_no

See also

SELECT

8.10.2. COUNT()

Available in

DSQL, ESQL, PSQL

Syntax

COUNT ([ALL | DISTINCT] <expr> | *)

Result type

Integer

Description

COUNT returns the number of non-null values in a group.

• ALL is the default: it simply counts all values in the set that are not NULL.

• If DISTINCT is specified, duplicates are excluded from the counted set.

• If COUNT (*) is specified instead of the expression expr, all rows will be counted. COUNT (*) — 

  • does not accept parameters

  • cannot be used with the keyword DISTINCT

  • does not take an expr argument, since its context is column-unspecific by definition

  • counts each row separately and returns the number of rows in the specified table or group without omitting duplicate rows

  • counts rows containing NULL

• If the result set is empty or contains only NULL in the specified column[s], the returned count is zero.

Example

SELECT
  dept_no,
  COUNT(*) AS cnt,
  COUNT(DISTINCT name) AS cnt_name
FROM employee
GROUP BY dept_no

See also

SELECT.

8.10.3. LIST()

Available in

DSQL, PSQL

Changed in

2.5

Syntax

LIST ([ALL | DISTINCT] <expr> [, separator ])

Result type

BLOB

Description

LIST returns a string consisting of the non-NULL argument values in the group, separated either by a comma or by a user-supplied separator. If there are no non-NULL values (this includes the case where the group is empty), NULL is returned.

• ALL (the default) results in all non-NULL values being listed. With DISTINCT, duplicates are removed, except if expr is a BLOB.

• In Firebird 2.5 and up, the optional separator argument may be any string expression. This makes it possible to specify e.g. ascii_char(13) as a separator. (This improvement has also been backported to 2.1.4.)

• The expr and separator arguments support BLOBs of any size and character set.

• Date/time and numeric arguments are implicitly converted to strings before concatenation.

• The result is a text BLOB, except when expr is a BLOB of another subtype.

• The ordering of the list values is undefined — the order in which the strings are concatenated is determined by read order from the source set which, in tables, is not generally defined. If ordering is important, the source data can be pre-sorted using a derived table or similar.

Examples

1. Retrieving the list, order undefined:

   SELECT LIST (display_name, '; ') FROM GR_WORK;

2. Retrieving the list in alphabetical order, using a derived table:

   SELECT LIST (display_name, '; ')
   FROM (SELECT display_name
         FROM GR_WORK
         ORDER BY display_name);

See also

SELECT

8.10.4. MAX()

Available in

DSQL, ESQL, PSQL

Syntax

MAX ([ALL | DISTINCT] <expr>)

Result type

Returns a result of the same data type the input expression.

Description

MAX returns the maximum non-NULL element in the result set.

• If the group is empty or contains only NULLs, the result is NULL.

• If the input argument is a string, the function will return the value that will be sorted last if COLLATE is used.

• This function fully supports text BLOBs of any size and character set.

Example

SELECT
  dept_no,
  MAX(salary)
FROM employee
GROUP BY dept_no

See also

MIN(), SELECT

8.10.5. MIN()

Available in

DSQL, ESQL, PSQL

Syntax

MIN ([ALL | DISTINCT] <expr>)

Result type

Returns a result of the same data type the input expression.

Description

MIN returns the minimum non-NULL element in the result set.

• If the group is empty or contains only NULLs, the result is NULL.

• If the input argument is a string, the function will return the value that will be sorted first if COLLATE is used.

• This function fully supports text BLOBs of any size and character set.

Example

SELECT
  dept_no,
  MIN(salary)
FROM employee
GROUP BY dept_no

See also

MAX(), SELECT

8.10.6. SUM()

Available in

DSQL, ESQL, PSQL

Syntax

SUM ([ALL | DISTINCT] <expr>)

Result type

Returns a result of the same numeric data type as the input expression.

Description

SUM calculates and returns the sum of non-null values in the group.

• If the group is empty or contains only NULLs, the result is NULL.

• ALL is the default option — all values in the set that are not NULL are processed. If DISTINCT is specified, duplicates are removed from the set and the SUM evaluation is done afterwards.

Example

SELECT
  dept_no,
  SUM (salary),
FROM employee
GROUP BY dept_no

See also

SELECT