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SQL Expressions


Logical Comparisons


Introduction



For your databases, you can create expressions that represent a combination of values, variables, and operators. To support expressions, Transact-SQL provides operators other than, or in addition to, those we saw in Lesson 2.

A comparison is a Boolean operation that produces a true or a false result, depending on the values on which the comparison is performed. A comparison is performed between two values of the same type; for example, you can compare two numbers, two characters, or the names of two cities. To support comparisons, Transact-SQL provides all necessary operators.

Conditional Statements


Introduction


IF...ELSE



The IF condition we used above is appropriate when you only need to know if an expression is true. There is nothing to do in other alternatives. Consider the following code:

DECLARE @DateHired As DateTime,
@CurrentDate As DateTime
SET @DateHired = '1996/10/04'
SET @CurrentDate = '2007/04/16'
IF @DateHired > @CurrentDate
PRINT 'You have the experience required for a new promotion'
GO



source : http://blogs.msdn.com/sharepoint/default.aspx