hi
i am learning postgres and made a library model
i dont want a user to be able to borrow 2 items (copies)
of the same book so made a function to check it (below)
the function works fine but now i would like to add a constraint,
unfortunatelly i fail
here's my try:
create function bookborrow_check_insert
(bookborrow.userid%TYPE, bookborrow.bookitem_id%TYPE)
returns bool as
'select NOT $1 in (select userid from bookborrow where userid = $1 and
bookitem_id = $2 and returned is null)'
language sql;
=> alter table bookborrow add check(bookborrow_check_insert (userid, bookitem_id));
ERROR: AlterTableAddConstraint: rejected due to CHECK constraint <unnamed>
=> alter table bookborrow add constraint check_insert check(bookborrow_check_insert (userid, bookitem_id));
ERROR: AlterTableAddConstraint: rejected due to CHECK constraint check_insert
--
Michal Adamczak
pokryfka @ druid.if.uj.edu.pl
GS dpu C+++ UL+++++ L+++(++++) w--- !tv h*
I code AND I bathe. (seen on slashdot)
