Set Functions 

Set functions are aggregate functions (they return one value for groups of rows and therefore imply grouping of tables).

Syntax

<set function> ::= COUNT '(' '*' ')'                           | COUNT '(' DISTINCT <value expression> ')'                           | <general set function>. <general set function> ::=                    ( SUM | AVG | MIN | MAX )                   '(' ( DISTINCT | ALL )? <value expression> ')'.

 

The return type of set functions follow these rules:

·        COUNT: The return type is exact numeric with scale 0.

·        AVG: The return type is approximate numeric.

·        MIN, MAX, SUM: The return type is the type of the argument.

Examples

SELECT AVG(salary) FROM employees

Average. This query determines the average salary of all employees.

SELECT COUNT(*) FROM employees

COUNT(*). This query determines the number of employees.

SELECT COUNT(DISTINCT employee_name) FROM employees

Average. This query determines the number of different names of the employees.

See

Value expressions