Aggregate functions

The following information applies to all aggregate functions other than COUNT(*) and COUNT_BIG(*).

The argument of an aggregate function is a set of values derived from an expression. The expression may include columns but cannot include another aggregate function. The scope of the set is a group or an intermediate result table as explained in Chapter 4, "Queries".
If a GROUP BY clause is specified in a query and the intermediate result of the FROM, WHERE, GROUP BY, and HAVING clauses is the empty set, then the aggregate functions are not applied, the result of the query is the empty set.
If a GROUP BY clause is not specified in a query and the intermediate result of the FROM, WHERE, and HAVING clauses is the empty set, then the aggregate functions are applied to the empty set. For example, the result of the following SELECT statement is applied to the empty set because department D01 has no employees:
```
  SELECT COUNT(DISTINCT JOB)
    FROM EMPLOYEE
    WHERE WORKDEPT = 'D01'
```
The keyword DISTINCT is not considered an argument of the function, but rather a specification of an operation that is performed before the function is applied. If DISTINCT is specified, redundant duplicate values are eliminated. If ALL is implicitly or explicitly specified, redundant duplicate values are not eliminated.
An aggregate function can be used in a WHERE clause only if that clause is part of a subquery of a HAVING clause and the column name specified in the expression is a correlated reference to a group. If the expression includes more than one column name, each column name must be a correlated reference to the same group.

AVG

           .-ALL------.
>>-AVG--(--+----------+--numeric-expression--)-----------------><
           '-DISTINCT-'

The AVG function returns the average of a set of numbers.

numeric-expression: The argument values must be any built-in numeric data type and their sum must be within the range of the data type of the result.

The data type of the result is the same as the data type of the argument values, except that:

The result is double-precision floating point if the argument values are single-precision floating point.
The result is large integer if the argument values are small integers.
The result is decimal if the argument values are decimal or nonzero scale binary with precision p and scale s. The precision of the result is p-s+ min(ms, mp-p+s). The scale of the result is min(ms, mp-p+s).

For information on the values of p, s, ms, and mp, see Decimal arithmetic in SQL.

The function is applied to the set of values derived from the argument values by the elimination of null values. If DISTINCT is used, duplicate values are eliminated.

The result can be null. If set of values is empty, the result is the null value. Otherwise, the result is the average value of the set.

The order in which the values are aggregated is undefined, but every intermediate result must be within the range of the result data type.

If the type of the result is integer, the fractional part of the average is lost.

Examples

Using the PROJECT table, set the host variable AVERAGE (DECIMAL(5,2)) to the average staffing level (PRSTAFF) of projects in department (DEPTNO) 'D11'.
```
     SELECT AVG(PRSTAFF)
       INTO :AVERAGE
       FROM PROJECT
       WHERE DEPTNO = 'D11'
```
Results in AVERAGE being set to 4.25 (that is, 17/4).
Using the PROJECT table, set the host variable ANY_CALC to the average of each unique staffing value (PRSTAFF) of projects in department (DEPTNO) 'D11'.
```
     SELECT AVG(DISTINCT PRSTAFF)
       INTO :ANY_CALC
       FROM PROJECT
       WHERE DEPTNO = 'D11'
```
Results in ANY_CALC being set to 4.66 (that is, 14/3).

COUNT

               .-ALL------.
>>-COUNT--(--+-+----------+--expression-+--)-------------------><
             | '-DISTINCT-'             |
             '-*------------------------'

The COUNT function returns the number of rows or values in a set of rows or values.

expression: The argument values can be of any built-in data type other than a DataLink. If DISTINCT is used, the resulting expression must not have a length attribute greater than 2000 for a character column or 1000 for a graphic column, and must not be a LOB.

The result of the function is a large integer and it must be within the range of large integers. The result cannot be null. If the table is a distributed table, then the result is DECIMAL(15,0). For more information about distributed tables, see the DB2® Multisystem book.

The argument of COUNT(*) is a set of rows. The result is the number of rows in the set. A row that includes only null values is included in the count.

The argument of COUNT(expression) or COUNT(ALL expression) is a set of values. The function is applied to the set derived from the argument values by the elimination of null values. The result is the number of non-null values in the set including duplicates.

The argument of COUNT(DISTINCT expression) is a set of values. The function is applied to the set of values derived from the argument values by the elimination of null values and duplicate values. The result is the number of values in the set.

If a sort sequence other than *HEX is in effect when the statement that contains the COUNT(DISTINCT expression) is executed and the arguments are SBCS data, mixed data, or Unicode data, then the result is obtained by comparing weighted values for each value in the set. The weighted values are based on the sort sequence.

Examples

Using the EMPLOYEE table, set the host variable FEMALE (INTEGER) to the number of rows where the value of the SEX column is 'F'.
```
   SELECT COUNT(*)
     INTO :FEMALE
     FROM EMPLOYEE
     WHERE SEX = 'F'
```
Results in FEMALE being set to 19.
Using the EMPLOYEE table, set the host variable FEMALE_IN_DEPT (INTEGER) to the number of departments (WORKDEPT) that have at least one female as a member.
```
     SELECT COUNT(DISTINCT WORKDEPT)
       INTO :FEMALE_IN_DEPT
       FROM EMPLOYEE
       WHERE SEX='F'
```
Results in FEMALE_IN_DEPT being set to 6. (There is at least one female in departments A00, C01, D11, D21, E11, and E21.)

COUNT_BIG

                   .-ALL------.
>>-COUNT_BIG--(--+-+----------+--expression-+--)---------------><
                 | '-DISTINCT-'             |
                 '-*------------------------'

The COUNT_BIG function returns the number of rows or values in a set of rows or values. It is similar to COUNT except that the result can be greater than the maximum value of integer.

expression: The argument values can be of any built-in data type other than a DataLink. If DISTINCT is used, the resulting expression must not have a length attribute greater than 2000 for a character column or 1000 for a graphic column, and must not be a LOB.

The result of the function is a decimal with precision 31 and scale 0. The result cannot be null.

The argument of COUNT_BIG(*) is a set of rows. The result is the number of rows in the set. A row that includes only null values is included in the count.

The argument of COUNT_BIG(expression) is a set of values. The function is applied to the set derived from the argument values by the elimination of null values. The result is the number of values in the set.

If a sort sequence other than *HEX is in effect when the statement that contains the COUNT_BIG(DISTINCT expression) is executed and the arguments are SBCS data, mixed data, or Unicode data, then the result is obtained by comparing weighted values for each value in the set. The weighted values are based on the sort sequence.

Examples

Refer to COUNT examples and substitute COUNT_BIG for occurrences of COUNT. The results are the same except for the data type of the result.
To count on a specific column, a sourced function must specify the type of the column. In this example, the CREATE FUNCTION statement creates a sourced function that takes any column defined as CHAR, uses COUNT_BIG to perform the counting, and returns the result as a double precision floating-point number. The query shown counts the number of unique departments in the sample employee table.
```
     CREATE FUNCTION RICK.COUNT(CHAR()) RETURNS DOUBLE
       SOURCE QSYS2.COUNT_BIG(CHAR());

     SET CURRENT PATH RICK, SYSTEM PATH 

     SELECT COUNT(DISTINCT WORKDEPT FROM EMPLOYEE;
```
The empty parenthesis in the parameter list for the new function (RICK.COUNT) means that the input parameter for the new function is the same type as the input parameter for the function named in the SOURCE clause. The empty parenthesis in the parameter list in the SOURCE clause (COUNT_BIG) means that the length attribute of the CHAR parameter of the COUNT_BIG function is ignored when DB2 locates the COUNT_BIG function.

MAX

           .-ALL------.
>>-MAX--(--+----------+--expression--)-------------------------><
           '-DISTINCT-'

The MAX aggregate function returns the maximum value in a set of values in a group.

expression: The argument values can be any built-in data types except LOB and DataLink values.

The data type and length attribute of the result are the same as the data type and length attribute of the argument values. When the argument is a string, the result has the same CCSID as the argument.

If a sort sequence other than *HEX is in effect when the statement that contains the MAX function is executed and the arguments are SBCS data, mixed data, or Unicode data, then the result is obtained by comparing weighted values for each value in the set. The weighted values are based on the sort sequence.

The function is applied to the set of values derived from the argument values by the elimination of null values.

The result can be null. If the function is applied to the empty set, the result is a null value. Otherwise, the result is the maximum value in the set.

The specification of DISTINCT has no effect on the result and is not advised.

Examples

Using the EMPLOYEE table, set the host variable MAX_SALARY (DECIMAL(7,2)) to the maximum monthly salary (SALARY / 12) value.
```
     SELECT MAX(SALARY) /12
       INTO :MAX_SALARY
       FROM EMPLOYEE
```
Results in MAX_SALARY being set to 4395.83.
Using the PROJECT table, set the host variable LAST_PROJ (CHAR(24)) to the project name (PROJNAME) that comes last in the sort sequence.
```
     SELECT MAX(PROJNAME)
       INTO :LAST_PROJ
       FROM PROJECT
```
Results in LAST_PROJ being set to 'WELD LINE PLANNING '.

MIN

           .-ALL------.
>>-MIN--(--+----------+--expression--)-------------------------><
           '-DISTINCT-'

The MIN aggregate function returns the minimum value in a set of values in a group.

expression: The argument values can be any built-in data types except LOB and DataLink values.

If a sort sequence other than *HEX is in effect when the statement that contains the MIN function is executed and the arguments are SBCS data, mixed data, or Unicode data, then the result is obtained by comparing weighted values for each value in the set.

The function is applied to the set of values derived from the argument values by the elimination of null values.

If the function is applied to the empty set, the result is a null value. Otherwise, the result is the minimum value in the set.

The specification of DISTINCT has no effect on the result and is not advised.

Examples

Using the EMPLOYEE table, set the host variable COMM_SPREAD (DECIMAL(7,2)) to the difference between the maximum and minimum commission (COMM) for the members of department (WORKDEPT) 'D11'.
```
     SELECT MAX(COMM) - MIN(COMM)
       INTO :COMM_SPREAD
       FROM EMPLOYEE
       WHERE WORKDEPT  = 'D11'
```
Results in COMM_SPREAD being set to 1118 (that is, 2580 - 1462).
Using the PROJECT table, set the host variable FIRST_FINISHED (CHAR(10)) to the estimated ending date (PRENDATE) of the first project scheduled to be completed.
```
     SELECT MIN(PRENDATE)
       INTO :FIRST_FINISHED
       FROM PROJECT
```
Results in FIRST_FINISHED being set to '1982-09-15'.

STDDEV_POP or STDDEV

                      .-ALL------.
>>-+-STDDEV_POP-+--(--+----------+--numeric-expression--)------><
   '-STDDEV-----'     '-DISTINCT-'

The STDDEV_POP function returns the biased standard deviation (/n) of a set of numbers. The formula used to calculate the biased standard deviation is:

STDDEV_POP = SQRT(VAR_POP)

where SQRT(VAR_POP) is the square root of the variance.

numeric-expression: The argument values must be any built-in numeric data type.

The data type of the result is double-precision floating point.

The function is applied to the set of values derived from the argument values by the elimination of null values. If DISTINCT is specified, duplicate values are eliminated.

The result can be null. If the function is applied to the empty set, the result is a null value. Otherwise, the result is the standard deviation of the values in the set.

The order in which the values are added is undefined, but every intermediate result must be within the range of the result data type.

Note

Syntax alternatives: STDEV_POP should be used for conformance to the SQL 1999 standard.

Example

Using the EMPLOYEE table, set the host variable DEV (double-precision floating point) to the standard deviation of the salaries for those employees in department A00.
```
   SELECT STDDEV_POP(SALARY)
     INTO :DEV
     FROM EMPLOYEE
     WHERE WORKDEPT = 'A00';
```
Results in DEV being set to approximately 9742.43.

STDDEV_SAMP

                   .-ALL------.
>>-STDDEV_SAMP--(--+----------+--numeric-expression--)---------><
                   '-DISTINCT-'

The STDDEV_SAMP function returns the sample standard deviation (/n-1) of a set of numbers. The formula used to calculate the sample standard deviation is:

STDDEV_SAMP = SQRT(VAR_SAMP)

where SQRT(VAR_SAMP) is the square root of the sample variance.

numeric-expression: The argument values must be any built-in numeric data type.

The data type of the result is double-precision floating point.

The function is applied to the set of values derived from the argument values by the elimination of null values. If DISTINCT is specified, duplicate values are eliminated.

The result can be null. If the function is applied to the empty set or a set with only one row, the result is a null value. Otherwise, the result is the standard deviation of the values in the set.

The order in which the values are added is undefined, but every intermediate result must be within the range of the result data type.

Example

Using the EMPLOYEE table, set the host variable DEV (double-precision floating point) to the sample standard deviation of the salaries for those employees in department A00.
```
   SELECT STDDEV_SAMP(SALARY)
     INTO :DEV
     FROM EMPLOYEE
     WHERE WORKDEPT = 'A00';
```
Results in DEV being set to approximately 10892.37.

SUM

           .-ALL------.
>>-SUM--(--+----------+--numeric-expression--)-----------------><
           '-DISTINCT-'

The SUM function returns the sum of a set of numbers.

numeric-expression: The argument values must be any built-in numeric data type.

The data type of the result is the same as the data type of the argument values except that the result is:

A double-precision floating point if the argument values are single-precision floating point
A large integer if the argument values are small integers
A decimal with precision mp and scale s if the argument values are decimal or nonzero scale binary numbers with precision p and scale s.

For information on the values of p, s, and mp, see Decimal arithmetic in SQL.

The function is applied to the set of values derived from the argument values by the elimination of null values. If DISTINCT is specified, duplicate values are eliminated.

The result can be null. If the function is applied to the empty set, the result is a null value. Otherwise, the result is the sum of the values in the set.

The order in which the values are added is undefined, but every intermediate result must be within the range of the result data type.

Example

Using the EMPLOYEE table, set the host variable JOB_BONUS (DECIMAL(9,2)) to the total bonus (BONUS) paid to clerks (JOB='CLERK').
```
   SELECT SUM(BONUS)
     INTO :JOB_BONUS
     FROM EMPLOYEE
     WHERE JOB = 'CLERK'
```
Results in JOB_BONUS being set to 4000.

VAR_POP or VARIANCE or VAR

                    .-ALL------.
>>-+-VAR_POP--+--(--+----------+--numeric-expression--)--------><
   +-VARIANCE-+     '-DISTINCT-'
   '-VAR------'

The VAR_POP function returns the biased variance (/n) of a set of numbers. The formula used to calculate the biased variance is:

   VAR_POP = SUM(X**2)/COUNT(X) - (SUM(X)/COUNT(X))**2

numeric-expression: The argument values must be any built-in numeric data type.

The data type of the result is double-precision floating point.

The function is applied to the set of values derived from the argument values by the elimination of null values. If DISTINCT is specified, duplicate values are eliminated.

The result can be null. If the function is applied to the empty set, the result is a null value. Otherwise, the result is the variance of the values in the set.

The order in which the values are added is undefined, but every intermediate result must be within the range of the result data type.

Note

Syntax alternatives: VAR_POP should be used for conformance to the SQL 1999 standard.

Example

Using the EMPLOYEE table, set the host variable VARNCE (double-precision floating point) to the variance of the salaries for those employees in department A00.
```
     SELECT VAR_POP(SALARY)
       INTO :VARNCE
       FROM EMPLOYEE
       WHERE WORKDEPT = 'A00';
```
Results in VARNCE being set to approximately 94 915 000.

VARIANCE_SAMP or VAR_SAMP

                         .-ALL------.
>>-+-VAR_SAMP------+--(--+----------+--numeric-expression--)---><
   '-VARIANCE_SAMP-'     '-DISTINCT-'

The VAR_SAMP function returns the sample variance (/n-1) of a set of numbers. The formula used to calculate the sample variance is:

   VAR_SAMP = (SUM(X**2) - ((SUM(X)**2) / (COUNT(*)))) / (COUNT(*) - 1)

numeric-expression: The argument values must be any built-in numeric data type.

The data type of the result is double-precision floating point.

The function is applied to the set of values derived from the argument values by the elimination of null values. If DISTINCT is specified, duplicate values are eliminated.

The result can be null. If the function is applied to the empty set or a set with only one row, the result is a null value. Otherwise, the result is the variance of the values in the set.

The order in which the values are added is undefined, but every intermediate result must be within the range of the result data type.

Note

Syntax alternatives: VAR_SAMP should be used for conformance to the SQL 1999 standard.

Example

Using the EMPLOYEE table, set the host variable VARNCE (double-precision floating point) to the sample variance of the salaries for those employees in department A00.
```
     SELECT VAR_SAMP(SALARY)
       INTO :VARNCE
       FROM EMPLOYEE
       WHERE WORKDEPT = 'A00';
```
Results in VARNCE being set to approximately 1 186 437 500.

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