How Can I Implement IF-THEN Logic in SQL SELECT Statements?

Implement IF-THEN logic in SQL SELECT statement

A common need in SQL programming is to perform condition checks and return different results based on the results. This article will explore how to implement IF...THEN logic in a SQL SELECT statement.

Use CASE statement

The CASE statement is equivalent to the IF statement in SQL. It allows you to specify multiple conditions and corresponding actions.

SELECT CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ELSE result3
END AS conditional_column, *
FROM table_name

For example, to check if a product is salable based on its Obsolete and InStock values:

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

Use IIF statement (SQL Server 2012 and above)

The IIF statement introduced in SQL Server 2012 simplifies the syntax of conditional statements. Its format is as follows:

SELECT IIF(condition, result_if_true, result_if_false) AS conditional_column, *
FROM table_name

The above example can be rewritten using the IIF statement as:

SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Saleable, *
FROM Product

Other instructions

• CASE statements can be nested to handle more complex conditions.
• The CAST operator can be used to convert the result to a specific data type, such as Boolean.
• Nested CASE statements and IIF statements can be included in aggregate functions.

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