Peter Fein <pfein@xxxxxxxxx> writes: > Let's say I have a base table B (with a PK id, say) and two derived > tables D1 & D2 (with different cols). For a given B.id, I'd like to > allow only a corresponding row in *either* D1 or D2, but not both. Any > suggestions on how to do this? Should I not be using inheritance at all? > My thought was to add a column inherits_to to B with a value indicating > whether that row is really a D1 or a D2 and enforce it with appropriate > CHECK constraints on each of the derived tables. If it can only be one or the other, I think you're misdesigning the thing. Use *one* table with all the columns needed to describe either a D1 or D2. Leave the unneeded columns NULL in any given row. (If needed, you can have a check constraint that specifies that certain columns are not null when it's a D1, etc.) Null entries are cheap. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to majordomo@xxxxxxxxxxxxxx
