What Are Logical/Boolean Operations in SQL Server Transact-SQL?

Logical (Boolean) operations are performed on Boolean values with logical operators like 'AND', 'OR', or 'NOT'. Logical operations return Boolean values. SQL Server 2005 supports the following logical operations:

• AND - Returns TRUE if both operands are TRUE.
• OR - Returns TRUE if one of the operands is TRUE.
• NOT - Returns TRUE if the only operand is FALSE.

Logical operations are commonly used to combine Boolean values resulted from comparison operations. The following tutorial exercise shows you a good example:

DECLARE @income MONEY;
DECLARE @marriage_status VARCHAR(10);
SET @income = 55000.00;
SET @marriage_status = 'Single';
SELECT CASE WHEN 
         (@marriage_status = 'Married' AND @income < 65000)
      OR (@marriage_status = 'Single' AND @income < 35000)
   THEN 'Qualified for the benefit.'
   ELSE 'Not qualified for the benefit.'
   END;
GO
Not qualified for the benefit.

⇒Boolean Values and Logical Operations in SQL Server Transact-SQL

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