case … when … (simple)


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Case is a conditional SQL expression: It searches for the first when clause whose value equals (=) that of the case clause and returns the value of the corresponding then clause—or that of else if nothing matches or null if there is no else clause.

SELECT CASE <expr> WHEN 0 THEN 'zero'
                   WHEN 1 THEN 'one'
                   ELSE 'not zero or one'
        END
  FROM …

Note that when null never matches. Use case when <expr> is null instead.

Normative References

The simple case expression is defined in ISO/IEC 9075-2:2023 as mandatory feature F261-01.

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