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.

<code class="language-sql">SELECT CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ELSE result3
END AS conditional_column, *
FROM table_name</code>

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

<code class="language-sql">SELECT CAST(
    CASE
        WHEN Obsolete = 'N' OR InStock = 'Y'
        THEN 1
        ELSE 0
    END AS bit) AS Saleable, *
FROM Product</code>

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:

<code class="language-sql">SELECT IIF(condition, result_if_true, result_if_false) AS conditional_column, *
FROM table_name</code>

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

<code class="language-sql">SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Saleable, *
FROM Product</code>

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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