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Aggregate Functions In SQL Server

In this article, we will discuss aggregate function in SQL Server.

Purpose

Aggregate functions perform a calculation on set of values and return a single value. SQL Server has given many aggregate functions to perform different operations.

In this article, we will discuss about 4 aggregate functions: -

Sum
Avg
Max
Count

To illustrate the functions, we will create a dummy table and execute query one by one.

Student, Subject and Marks tables

Student_ID	Student_Name
1	Karan
2	Sumit
3	Ashish

Subject_ID	Subject_Name
1	Mathematics
2	Social Studies
3	General Science

Primary_Key_ID	Student_ID	Subject_ID	Marks
1	1	1	85
2	1	2	65
3	1	3	60

Sum

select sum(Marks) from Marks where Student_ID = 1

If you look at the above query closely, the "Sum" function contains the column name of the table on which calculation needs to be done. The output would of this query is 210(85 + 65 + 60).

Avg

select avg(Marks) from Marks where Student_ID = 1

output – 70((85 + 65 + 60)/3)

Max

select max(Marks) from Marks where Student_ID = 1

output- 85 because out of 3 marks 85 is the highest one.

Count

select count(*) from department where Student_ID = 1

output – 3 because there are three records that satisfies the above condition.

Posted By -	Karan Gupta

Posted On -	Monday, March 29, 2010

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