COUNT function [Aggregate]

Counts the number of rows in a group depending on the specified parameters.

Syntax 1
COUNT( 
*
| expression
|  DISTINCT expression 
)
Syntax 2
COUNT( 
{ * | expression }
) OVER ( window-spec )
window-spec : see Syntax 2 instructions in the Remarks section below
Parameters
  • *   Return the number of rows in each group.

  • expression   The expression for which to return the number of rows.

  • DISTINCT expression   The expression for which to return the number of distinct rows.

Returns

INT

Remarks

Rows where the value is the NULL value are not included in the count.

Syntax 2 represents usage as a window function in a SELECT statement. As such, elements of window-spec can be specified either in the function syntax (inline), or in conjunction with a WINDOW clause in the SELECT statement. See the window-spec definition provided in WINDOW clause.

For more information about using window functions in SELECT statements, including working examples, see Window functions.

See also
Standards and compatibility
  • SQL/2003   Core feature. Syntax 2 is feature T611.

Example

The following statement returns each unique city, and the number of rows with that city value.

SELECT City, COUNT( * ) FROM Employees GROUP BY City;