On 7 Aug 2003, Neil Zanella wrote:
> of transactions as opposed to the operations taking place serially? Also, does
> PostgreSQL fully support SQL99 CHECK constraints? And if the system crashes...
Technically no. Check constraints with subselects are not supported.
Using a function gets you half the constraint, but doesn't notice
modifications to the other table(s) involved. You might need triggers
to handle that portion.