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.
Related
Tutorial:
Case— Conditional ExpressionsOther conditional SQL expressions
Product specific features:
if,decode.
Normative References
The simple case expression is defined in ISO/IEC 9075:2016-2 as mandatory feature F261-01.
