On Wed, Apr 25, 2012 at 11:33 AM, <atrig...@ccs.neu.edu> wrote: > Seeing as Postgres does not allow sub-queries in CHECK constraints yet, it > doesn't make any sense to me for it to allow function calls, since functions > can perform queries.
This is why functions must be marked as one of VOLATILE, STABLE, or IMMUTABLE. Only IMMUTABLE functions can be used in CHECK constraints. It's a feature that expressions including subqueries are automatically detected as not being immutable and automatically barred. Functions do not have this feature and must be manually marked by the user with the correct state. This is a useful escape hatch in cases where an expression can not be proven to be immutable but the user knows that due to the design of his or her application it is in fact immutable -- for instance queries that query from tables that the user is certain will never be modified. The database cannot detect every possible erroneous usage, at least not without being less useful. It's a balancing act of providing the user with as many safety nets as possible without imposing too many restrictions. Too many safety nets and you can't do some things, too few and you spend too much time checking for or debugging problems. -- greg -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs
