9.13.1. CASE
The SQL CASE expression is a generic conditional expression, similar to if/else statements in other languages:
CASE WHEN condition THEN result
[WHEN ...]
[ELSE result]
END
CASE clauses can be used wherever an expression is valid. condition is an expression that returns a
boolean result. If the result is true then the value of the CASE expression is the result that follows the
condition. If the result is false any subsequent WHEN clauses are searched in the same manner. If no WHEN
condition is true then the value of the case expression is the result in the ELSE clause. If the ELSE
clause is omitted and no condition matches, the result is null.
An example:
SELECT * FROM test;
a
---
1
2
3
SELECT a,
CASE WHEN a=1 THEN ’one’
WHEN a=2 THEN ’two’
ELSE ’other’
END
FROM test;
a | case
---+-------
1 | one
2 | two
3 | other