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WHILE (Transact-SQL)

 

THIS TOPIC APPLIES TO: yesSQL Server (starting with 2008)yesAzure SQL DatabaseyesAzure SQL Data Warehouse yesParallel Data Warehouse

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.

Topic link icon Transact-SQL Syntax Conventions

  
WHILE Boolean_expression   
     { sql_statement | statement_block | BREAK | CONTINUE }  
  

-- Azure SQL Data Warehouse and Parallel Data Warehouse  
WHILE Boolean_expression   
     { sql_statement | statement_block | BREAK }  
  

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.

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.

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

C: Simple While Loop

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.

-- 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  
  

ALTER TRIGGER (Transact-SQL)
Control-of-Flow Language (Transact-SQL)
CREATE TRIGGER (Transact-SQL)
Cursors (Transact-SQL)
SELECT (Transact-SQL)

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