SQL WHEN: Purpose and Usage Guide

1 year ago
Isabella Edwards
1 minute

In SQL, “WHEN” is used for expressing conditions in statements.

“WHEN” is typically used in conjunction with a “CASE” statement to specify conditions and return results. It can be used to define multiple conditions within a “CASE” statement and return different results based on the satisfied conditions.

The grammar is as follows:

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

The condition following “WHEN” is a boolean expression, and if the condition is met, the corresponding result is returned. If none of the conditions are met and an ELSE is specified, the result after ELSE is returned. When there are multiple “WHEN” conditions in a “CASE” statement, they are evaluated sequentially, and only the first condition that is met will be executed, while the others will be ignored.

The purpose of “WHEN” is to determine the result based on the conditions, allowing SQL query results to be customized according to different criteria.

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