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 inDSQL, ESQL, PSQL

Syntax

  |AVG ([ALL | DISTINCT] <expr>)

Table 8.66. AVG Function Parameters

Parameter	Description
expr	Expression. It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF that returns a numeric data type. Aggregate functions are not allowed as expressions

Result typeA numeric data type, the same as the data type of the argument.

DescriptionAVG 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

8.10.2. `COUNT()`

Available inDSQL, ESQL, PSQL

Syntax

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

Table 8.67. COUNT Function Parameters

Parameter	Description
expr	Expression. It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF that returns a numeric data type. Aggregate functions are not allowed as expressions

Result typeInteger

DescriptionCOUNT 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

8.10.3. `LIST()`

Available inDSQL, PSQL

Changed in2.5

Syntax

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

Table 8.68. LIST Function Parameters

Parameter	Description
expr	Expression. It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF that returns the string data type or a `BLOB`. Fields of numeric and date/time types are converted to strings. Aggregate functions are not allowed as expressions.
separator	Optional alternative separator, a string expression. Comma is the default separator

Result typeBLOB

DescriptionLIST 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.
⚠
Caution
This is a trick/workaround, and it depends on implementation details of the optimizer/execution order. This trick doesn’t always work, and it is not guaranteed to work across versions.

Examples

Retrieving the list, order undefined:

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

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);

8.10.4. `MAX()`

Available inDSQL, ESQL, PSQL

Syntax

  |MAX ([ALL | DISTINCT] <expr>)

Table 8.69. MAX Function Parameters

Parameter	Description
expr	Expression. It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF. Aggregate functions are not allowed as expressions.

Result typeReturns a result of the same data type the input expression.

DescriptionMAX 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.

ⓘ

Note

The DISTINCT parameter makes no sense if used with MAX() and is implemented only for compliance with the standard.

Example

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

8.10.5. `MIN()`

Available inDSQL, ESQL, PSQL

Syntax

  |MIN ([ALL | DISTINCT] <expr>)

Table 8.70. MIN Function Parameters

Parameter	Description
expr	Expression. It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF. Aggregate functions are not allowed as expressions.

Result typeReturns a result of the same data type the input expression.

DescriptionMIN 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.

ⓘ

Note

The DISTINCT parameter makes no sense if used with MIN() and is implemented only for compliance with the standard.

Example

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

8.10.6. `SUM()`

Available inDSQL, ESQL, PSQL

Syntax

  |SUM ([ALL | DISTINCT] <expr>)

Table 8.71. SUM Function Parameters

Parameter	Description
expr	Numeric expression. It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF. Aggregate functions are not allowed as expressions.

Result typeDepends on the input type

DescriptionSUM 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 afterward.

The result type of SUM depends on the input type:

`FLOAT, DOUBLE PRECISION`	`DOUBLE PRECISION`
`SMALLINT, INTEGER, BIGINT`	`BIGINT`
`DECIMAL/NUMERIC(p, n)`	`DECIMAL/NUMERIC(18, n)`

Example

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

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