Overlapping WHEN clauses - who wins?

Question

Accepted Answer

The SQL standard guarantees that CASE evaluates WHEN clauses in the order they are written and stops at the first one that is TRUE. This is different from WHERE predicates, which a database optimizer can evaluate in any order for performance. The guaranteed order is why writing WHEN amount < 100 before WHEN amount < 500 works correctly - once the first branch fires, later ones are never reached.