Picking a fallback phone number

Question

Accepted Answer

COALESCE evaluates its arguments left to right and returns the first one that is not NULL. Row 1: mobile is not NULL -> 555-1111. Row 2: mobile is NULL, home is NULL, work is not NULL -> 555-2222. Row 3: mobile is NULL, home is not NULL -> 555-3333. COALESCE(a, b, c) is exactly equivalent to CASE WHEN a IS NOT NULL THEN a WHEN b IS NOT NULL THEN b ELSE c END - it is standard SQL shorthand for that pattern.