WHILE (Transact-SQL)

Article
05/23/2023

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

Sets a condition for the repeated execution of an SQL statement or statement block. The statements are executed repeatedly as long as the specified condition is true. The execution of statements in the WHILE loop can be controlled from inside the loop with the BREAK and CONTINUE keywords.

Transact-SQL syntax conventions

Syntax

-- Syntax for SQL Server and Azure SQL Database and Microsoft Fabric
  
WHILE Boolean_expression   
     { sql_statement | statement_block | BREAK | CONTINUE }

-- Syntax for Azure Azure Synapse Analytics and Parallel Data Warehouse  
  
WHILE Boolean_expression   
     { sql_statement | statement_block | BREAK }

Note

To view Transact-SQL syntax for SQL Server 2014 and earlier, see Previous versions documentation.

Arguments

Boolean_expression
Is an expression that returns TRUE or FALSE. If the Boolean expression contains a SELECT statement, the SELECT statement must be enclosed in parentheses.

{sql_statement | statement_block}
Is any Transact-SQL statement or statement grouping as defined with a statement block. To define a statement block, use the control-of-flow keywords BEGIN and END.

BREAK
Causes an exit from the innermost WHILE loop. Any statements that appear after the END keyword, marking the end of the loop, are executed.

CONTINUE
Causes the WHILE loop to restart, ignoring any statements after the CONTINUE keyword.

Remarks

If two or more WHILE loops are nested, the inner BREAK exits to the next outermost loop. All the statements after the end of the inner loop run first, and then the next outermost loop restarts.

Examples

A. Using BREAK and CONTINUE with nested IF...ELSE and WHILE

In the following example, if the average list price of a product is less than $300, the WHILE loop doubles the prices and then selects the maximum price. If the maximum price is less than or equal to $500, the WHILE loop restarts and doubles the prices again. This loop continues doubling the prices until the maximum price is greater than $500, and then exits the WHILE loop and prints a message.

USE AdventureWorks2012;  
GO  
WHILE (SELECT AVG(ListPrice) FROM Production.Product) < $300  
BEGIN  
   UPDATE Production.Product  
      SET ListPrice = ListPrice * 2  
   SELECT MAX(ListPrice) FROM Production.Product  
   IF (SELECT MAX(ListPrice) FROM Production.Product) > $500  
      BREAK  
   ELSE  
      CONTINUE  
END  
PRINT 'Too much for the market to bear';

B. Using WHILE in a cursor

The following example uses @@FETCH_STATUS to control cursor activities in a WHILE loop.

DECLARE @EmployeeID as NVARCHAR(256)
DECLARE @Title as NVARCHAR(50)

DECLARE Employee_Cursor CURSOR FOR  
SELECT LoginID, JobTitle   
FROM AdventureWorks2012.HumanResources.Employee  
WHERE JobTitle = 'Marketing Specialist';  
OPEN Employee_Cursor;  
FETCH NEXT FROM Employee_Cursor INTO @EmployeeID, @Title;  
WHILE @@FETCH_STATUS = 0  
   BEGIN  
      Print '   ' + @EmployeeID + '      '+  @Title 
      FETCH NEXT FROM Employee_Cursor INTO @EmployeeID, @Title;  
   END;  
CLOSE Employee_Cursor;  
DEALLOCATE Employee_Cursor;  
GO

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

C: Simple While Loop

-- Uses AdventureWorks  
  
WHILE ( SELECT AVG(ListPrice) FROM dbo.DimProduct) < $300  
BEGIN  
    UPDATE dbo.DimProduct  
        SET ListPrice = ListPrice * 2;  
    SELECT MAX ( ListPrice) FROM dbo.DimProduct  
    IF ( SELECT MAX (ListPrice) FROM dbo.DimProduct) > $500  
        BREAK;  
END