TIMESTAMP is the "root" type of the temporal types and DECIMAL is the "root" type of numeric types (by "root", I mean the other types in that category are coercible to that type). So if you list just those two types, you're covered for DATE, TIME, TIMESTAMP, INTEGER, LONG, UNSIGNED_*). Also, when we support new types, like FLOAT & DOUBLE, you'll be covered for those as well.