How Can I Use Conditional Logic (IF-THEN) in SQL SELECT Statements?

Conditional Logic in SQL SELECT Statements: The CASE Statement

SQL employs the CASE statement to handle conditional logic within SELECT statements, offering a powerful alternative to traditional IF statements.

Implementing Conditional Logic with CASE

The CASE statement's fundamental structure is:

CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ...
    ELSE default_result
END

To illustrate, let's consider a scenario mirroring an IF...THEN construct:

SELECT
    CASE
        WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1
        ELSE 0
    END AS Saleable,
    *
FROM Product;

Further Considerations

• Data type conversion: The CAST operator can be utilized to explicitly convert the CASE statement's output to a Boolean (bit) data type if needed.
• Nested CASE statements and aggregate functions: CASE statements support nesting and can be effectively integrated within aggregate functions for complex conditional aggregations.
• IIF statement (SQL Server 2012 and later): SQL Server 2012 introduced the IIF statement, presenting an additional option for expressing conditional logic.

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