SQL Aggregate Functions

The SQL Server provides various Aggregate Functions, which allow us to perform aggregations such as calculating the average, sum, minimum, maximum, count, etc.

SQL Aggregate Functions

SQL Aggregate functions are used to extract the accumulated, total, or high-level data. For instance, the total sales in a region, product sales by country, etc. To use these SQL aggregate functions, you have to use the Group By Clause for the non-agg columns. Otherwise, it will throw an error.

The following table will show you the list of available Aggregate Functions. If you want to use any expressions to restrict the records, then use the Having Clause, not the Where Clause.

Functions	Description
AVG	It will calculate the Average of total records (or rows) selected by the SELECT Statement
CHECKSUM_AGG	It is used to return the checksum of the values in a Group
COUNT	It will Count the number of records selected by the SELECT Statement.
COUNT_BIG	It works same as the COUNT function, but it returns the bigint
GROUPING	It is used to indicate whether the specified column in a GROUP BY Clause aggregated or not
GROUPING_ID	This SQL Server function is used to return the level of grouping.
MAX	It returns the Maximum value from the selected total records.
MIN	It returns the Minimum value from the total rows selected.
STDEV	Calculates the Standard Deviation of the selected records
STDEVP	It is used to calculate the Standard Deviation for population
SUM	The Total or Sum of rows picked by the SELECT Statement
VAR	Statistical Variance of selected records
VARP	Statistical Variance for the population

Example

The following query will show you some SQL Server aggregate functions such as AVG, VAR, VARP, STDEV, STDEVP, SUM, MIN, MAX, and COUNT.

SELECT COUNT([EmployeeID]) AS [Total Employees]
      ,[Occupation]
      ,AVG([YearlyIncome]) AS [Average Income]
      ,VAR([YearlyIncome]) AS [Income Variance]
      ,VARP([YearlyIncome]) AS [Income Varp]
      ,STDEV([YearlyIncome]) AS [Income Deviation]
      ,STDEVP([YearlyIncome]) AS [Income stdevp]
      ,SUM([Sales]) AS [Total Sale]
      ,MIN([Sales]) AS [Minimum Sale]
      ,MAX([Sales]) AS [Maximum Sale]
      ,COUNT_BIG([DeptID]) AS [Dept Count_BIG]
  FROM [MyEmployees]
  GROUP BY [Occupation]

The remaining list of aggregate functions that includes Grouping, checksum_agg, and Grouping_id are:

SELECT [Education]
      ,[Occupation]
      ,GROUPING([Education]) AS 'Edu Grouping'
      ,GROUPING([Occupation]) AS 'Occ Grouping'
      ,GROUPING_ID([Education], [Occupation]) AS 'Grouping ID'
  	  ,CHECKSUM_AGG(DISTINCT CAST(DeptID AS INT)) AS [Unique Department ID] 
	  ,CHECKSUM_AGG(DISTINCT CAST([ManagerID] AS INT)) AS [Unique Manager ID]
FROM [MyEmployees]
GROUP BY [Education]
        ,[Occupation] WITH ROLLUP