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Transact-SQL Operators: WHILE
 

Introduction

To examine a condition and evaluate it before taking action, you can use the WHILE operator. The basic formula of this statement is:

WHILE Expression 
    Statement

When implementing this statement, first provide an Expression after the WHILE keyword. The Expression must produce a true or a false result. If the Expression is true, then the interpreter executes the Statement. After executing the Statement, the Expression is checked again. AS LONG AS the Expression is true, it will keep executing the Statement. When or once the Expression becomes false, it stops executing the Statement.

 This scenario can be illustrated as follows:

WHILE

Here is an example: 

DECLARE @Number As int

WHILE @Number < 5
	SELECT @Number AS Number
GO

To effectively execute a while condition, you should make sure you provide a mechanism for the interpreter to get a referenced value for the condition, variable, or expression being checked. This is sometimes in the form of a variable being initialized although it could be some other expression. Such a while condition could be illustrated as follows:

WHILE

This time, the statement would be implemented as follows:

DECLARE @Number As int
SET @Number = 1
WHILE @Number < 5
    BEGIN
	SELECT @Number AS Number
	SET @Number = @Number + 1
    END
GO

This would produce:

WHILE

   
 
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