STDEV (Transact-SQL)

Articol
09/03/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric

Returns the statistical standard deviation of all values in the specified expression.

Transact-SQL syntax conventions

Syntax

-- Aggregate Function Syntax   
STDEV ( [ ALL | DISTINCT ] expression )  
  
-- Analytic Function Syntax   
STDEV ([ ALL ] expression) OVER ( [ partition_by_clause ] order_by_clause)

Arguments

ALL
Applies the function to all values. ALL is the default.

DISTINCT
Specifies that each unique value is considered.

expression
Is a numeric expression. Aggregate functions and subqueries are not permitted. expression is an expression of the exact numeric or approximate numeric data type category, except for the bit data type.

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

Return Types

float

Remarks

If STDEV is used on all items in a SELECT statement, each value in the result set is included in the calculation. STDEV can be used with numeric columns only. Null values are ignored.

STDEV is a deterministic function when used without the OVER and ORDER BY clauses. It is nondeterministic when specified with the OVER and ORDER BY clauses. For more information, see Deterministic and Nondeterministic Functions.

Examples

A: Using STDEV

The following example returns the standard deviation for all bonus values in the SalesPerson table in the AdventureWorks2022 database.

SELECT STDEV(Bonus)  
FROM Sales.SalesPerson;  
GO

Examples: Azure Synapse Analytics and Analytics Platform System (PDW)

B: Using STDEV

The following example returns the standard deviation of the sales quota values in the table dbo.FactSalesQuota. The first column contains the standard deviation of all distinct values and the second column contains the standard deviation of all values including any duplicates values.

-- Uses AdventureWorks  
  
SELECT STDEV(DISTINCT SalesAmountQuota)AS Distinct_Values, STDEV(SalesAmountQuota) AS All_Values  
FROM dbo.FactSalesQuota;

Here's the result set.

Distinct_Values   All_Values
----------------  ----------------
398974.27         398450.57

C. Using STDEV with OVER

The following example returns the standard deviation of the sales quota values for each quarter in a calendar year. Notice that the ORDER BY in the OVER clause orders the STDEV and the ORDER BY of the SELECT statement orders the result set.

-- Uses AdventureWorks  
  
SELECT CalendarYear AS Year, CalendarQuarter AS Quarter, SalesAmountQuota AS SalesQuota,  
       STDEV(SalesAmountQuota) OVER (ORDER BY CalendarYear, CalendarQuarter) AS StdDeviation  
FROM dbo.FactSalesQuota  
WHERE EmployeeKey = 272 AND CalendarYear = 2002  
ORDER BY CalendarQuarter;