COUNT (Transact-SQL)

**APPLIES TO:** SQL Server (starting with 2008) Azure SQL Database Azure SQL Data Warehouse Parallel Data Warehouse

This function returns the number of items found in a group. COUNT operates like the COUNT_BIG function. These functions differ only in the data types of their return values. COUNT always returns an int data type value. COUNT_BIG always returns a bigint data type value.

Transact-SQL Syntax Conventions

Syntax

-- Aggregation Function Syntax  
COUNT ( { [ [ ALL | DISTINCT ] expression ] | * } )  

-- Analytic Function Syntax  
COUNT ( [ ALL ]  { expression | * } ) OVER ( [ <partition_by_clause> ] )  

Arguments

ALL
Applies the aggregate function to all values. ALL serves as the default.

DISTINCT
Specifies that COUNT returns the number of unique nonnull values.

expression
An expression of any type, except image, ntext, or text. Note that COUNT does not support aggregate functions or subqueries in an expression.

*
Specifies that COUNT should count all rows to determine the total table row count to return. COUNT(*) takes no parameters and does not support the use of DISTINCT. COUNT(*) does not require an expression parameter because by definition, it does not use information about any particular column. COUNT(*) returns the number of rows in a specified table, and it preserves duplicate rows. It counts each row separately. This includes rows that contain null values.

OVER ( [ partition_by_clause ] [ order_by_clause ] [ ROW_or_RANGE_clause ] )
The partition_by_clause divides the result set produced by the FROM clause into partitions to which the COUNT function is applied. If not specified, the function treats all rows of the query result set as a single group. The order_by_clause determines the logical order of the operation. See OVER Clause (Transact-SQL) for more information.

Return types

int

Remarks

COUNT(*) returns the number of items in a group. This includes NULL values and duplicates.

COUNT(ALL expression) evaluates expression for each row in a group, and returns the number of nonnull values.

COUNT(DISTINCT expression) evaluates expression for each row in a group, and returns the number of unique, nonnull values.

For return values exceeding 2^31-1, COUNT returns an error. For these cases, use COUNT_BIG instead.

COUNT is a deterministic function when used without the OVER and ORDER BY clauses. It is nondeterministic when used with the OVER and ORDER BY clauses. See Deterministic and Nondeterministic Functions for more information.

Examples

A. Using COUNT and DISTINCT

This example returns the number of different titles that an Adventure Works Cycles employee can hold.

SELECT COUNT(DISTINCT Title)  
FROM HumanResources.Employee;  
GO  

Here is the result set.

-----------
67  
  
(1 row(s) affected)

B. Using COUNT(*)

This example returns the total number of Adventure Works Cycles employees.

SELECT COUNT(*)  
FROM HumanResources.Employee;  
GO  

Here is the result set.

-----------
290  
  
(1 row(s) affected)

C. Using COUNT(*) with other aggregates

This example shows that COUNT(*) works with other aggregate functions in the SELECT list. The example uses the AdventureWorks2012 database.

SELECT COUNT(*), AVG(Bonus)  
FROM Sales.SalesPerson  
WHERE SalesQuota > 25000;  
GO  

Here is the result set.

----------- ---------------------
14            3472.1428
  
(1 row(s) affected)

D. Using the OVER clause

This example uses the MIN, MAX, AVG and COUNT functions with the OVER clause, to return aggregated values for each department in the AdventureWorks2012 database HumanResources.Department table.

SELECT DISTINCT Name  
       , MIN(Rate) OVER (PARTITION BY edh.DepartmentID) AS MinSalary  
       , MAX(Rate) OVER (PARTITION BY edh.DepartmentID) AS MaxSalary  
       , AVG(Rate) OVER (PARTITION BY edh.DepartmentID) AS AvgSalary  
       ,COUNT(edh.BusinessEntityID) OVER (PARTITION BY edh.DepartmentID) AS EmployeesPerDept  
FROM HumanResources.EmployeePayHistory AS eph  
JOIN HumanResources.EmployeeDepartmentHistory AS edh  
     ON eph.BusinessEntityID = edh.BusinessEntityID  
JOIN HumanResources.Department AS d  
ON d.DepartmentID = edh.DepartmentID
WHERE edh.EndDate IS NULL  
ORDER BY Name;  

Here is the result set.

Name                          MinSalary             MaxSalary             AvgSalary             EmployeesPerDept  
----------------------------- --------------------- --------------------- --------------------- ----------------  
Document Control              10.25                 17.7885               14.3884               5  
Engineering                   32.6923               63.4615               40.1442               6  
Executive                     39.06                 125.50                68.3034               4  
Facilities and Maintenance    9.25                  24.0385               13.0316               7  
Finance                       13.4615               43.2692               23.935                10  
Human Resources               13.9423               27.1394               18.0248               6  
Information Services          27.4038               50.4808               34.1586               10  
Marketing                     13.4615               37.50                 18.4318               11  
Production                    6.50                  84.1346               13.5537               195  
Production Control            8.62                  24.5192               16.7746               8  
Purchasing                    9.86                  30.00                 18.0202               14  
Quality Assurance             10.5769               28.8462               15.4647               6  
Research and Development      40.8654               50.4808               43.6731               4  
Sales                         23.0769               72.1154               29.9719               18  
Shipping and Receiving        9.00                  19.2308               10.8718               6  
Tool Design                   8.62                  29.8462               23.5054               6  
  
(16 row(s) affected)

Examples: [!INCLUDEssSDWfull] and [!INCLUDEssPDW]

E. Using COUNT and DISTINCT

This example returns the number of different titles that an employee of a specific company can hold.

USE ssawPDW;  
  
SELECT COUNT(DISTINCT Title)  
FROM dbo.DimEmployee;  

Here is the result set.

-----------
67

F. Using COUNT(*)

This example returns the total number of rows in the dbo.DimEmployee table.

USE ssawPDW;  
  
SELECT COUNT(*)  
FROM dbo.DimEmployee;  

Here is the result set.

-------------
296

G. Using COUNT(*) with other aggregates

This example combines COUNT(*) with other aggregate functions in the SELECT list. It returns the number of sales representatives with an annual sales quota greater than $500,000, and the average sales quota of those sales representatives.

USE ssawPDW;  
  
SELECT COUNT(EmployeeKey) AS TotalCount, AVG(SalesAmountQuota) AS [Average Sales Quota]  
FROM dbo.FactSalesQuota  
WHERE SalesAmountQuota > 500000 AND CalendarYear = 2001;  
  

Here is the result set.

TotalCount  Average Sales Quota
----------  -------------------
10          683800.0000

H. Using COUNT with HAVING

This example uses COUNT with the HAVING clause to return the departments of a company, each of which has more than 15 employees.

USE ssawPDW;  
  
SELECT DepartmentName,   
       COUNT(EmployeeKey)AS EmployeesInDept  
FROM dbo.DimEmployee  
GROUP BY DepartmentName  
HAVING COUNT(EmployeeKey) > 15;  

Here is the result set.

DepartmentName  EmployeesInDept
--------------  ---------------
Sales           18
Production      179

I. Using COUNT with OVER

This example uses COUNT with the OVER clause, to return the number of products contained in each of the specified sales orders.

USE ssawPDW;  
  
SELECT DISTINCT COUNT(ProductKey) OVER(PARTITION BY SalesOrderNumber) AS ProductCount  
    ,SalesOrderNumber  
FROM dbo.FactInternetSales  
WHERE SalesOrderNumber IN (N'SO53115',N'SO55981');  

Here is the result set.

ProductCount   SalesOrderID`
------------   -----------------
3              SO53115
1              SO55981

See also

Aggregate Functions (Transact-SQL)
COUNT_BIG (Transact-SQL)
OVER Clause (Transact-SQL)