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Aggregate functions in Database

Amit Singh4336 16-Nov-2010

Aggregate functions are applied to agroup of data values from a column. Aggregate functions always return a singlevalue.

How database supports following aggregate functions:

AVG: Calculates the arithmetic mean (average) of the data valuescontained within a column. The column must contain numeric values.

Syntax:

SELECTAVG(column_name) FROM table_name

MAX and MIN: Calculate the maximum and minimum data value of the column,respectively. The column can contain numeric, string, and date/time values.

Syntax:


SELECT MAX(column_name) FROM table_name
SELECT MIN(column_name) FROM table_name SUM: Calculates the total of all data values in a column. The columnmust contain numeric values.


Syntax:

SELECT SUM(column_name) FROM table_name

COUNT: Calculates the number of (non-null) data values in a column. Theonly aggregate function not being applied to columns is COUNT(*). This functionreturns the number of rows (whether or not particular columns have NULLvalues).

Syntax:

SELECT COUNT(column_name) FROM table_name

COUNT_BIG: New and Analogous to COUNT, the only difference being thatCOUNT_BIG returns a value of the BIGINT data type.

Syntax:

COUNT_BIG ( { [ ALL | DISTINCT ] expression } | * )

Aggregatefunction Example:


   SELECT COUNT(*)FROM tblcheck

Output:
CountData
9

·        SELECT SUM(empid) AS SumData  FROM tblcheck


Output:

SumData

45

Updated 18-Sep-2014

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