pá 29. 8. 2025 v 18:51 odesílatel Joel Jacobson <joel@compiler.org> napsal:
On Fri, Aug 29, 2025, at 18:17, Pavel Stehule wrote: >> >> I am not too serious now, I am just playing (and I remember this discussion many times). We can "theoretically" introduce new keyword `EXACT`, that can specify so any DML or SELECT can process or returns just one row (or with other clause zero rows) >> >> EXACT ONE SELECT id FROM tab WHERE id = 1; >> EXACT ONE UPDATE ... >> EXACT ONE DELETE ... >> EXACT ONE OR NONE SELECT ... > > or > > EXACT NONE SELECT ...
That would work, but I think I prefer CHECK DIAGNOSTICS (ROW_COUNT = 1), feels a bit more SQL-idiomatic, since there seems to already be a ROW_COUNT, and there is the concept of DIAGNOSTICS already, and CHECK feels natural.
I can also imagine ROW_COUNT with other values than 1 could be useful, e.g. ROW_COUNT = 2 to enforce inserting two transactions in a double-entry bookkeeping system.
In the meantime, maybe we want to add a catalog function nonnull(anyelement) -> anyelement that throws an error if the input is NULL? Seems like a function that could be useful in general. Attached a small patch that adds such a function.
