On Dec 3, 2004, at 4:04 PM, D. Richard Hipp wrote:
SQLite does not currently support recursive triggers. On of the main reasons for not supporting recursive triggers is that disallowing recursive triggers was seen as the easiest way to avoid infinite loops like this:
CREATE TRIGGER loop AFTER UPDATE OF table1 BEGIN UPDATE table1 SET cnt=(cnt+1)%100 WHERE rowid=old.rowid; END; UPDATE table1 SET cnt=1 WHERE rowid=1; -- Infinite loop
By disallowing recursive triggers, SQLite avoids the infinite loop above. But there are useful things one could do with recursive triggers that do not involve infinite loops. I would like to relax the constraint in SQLite and allow some support for recursive triggers as long as the recursive triggers do not cause an infinite loop. But I'm not sure how to do about it?
Question: What do other RDBMSes do with triggers that form infinite loops? Does anybody know?
Dynamic languages typically have a hard coded 'stack limit'. I think this is what Oracle does, see:
http://www.oreilly.com/catalog/ordevworkbook/chapter/ch16s.html #8
Use a 'stack limit' ;)Question: Can anybody suggest a way of providing support for recursive triggers which also guarantees that every SQL statement will eventually complete?
Report an error when the stack limit is reached. Unfortunately I don't know if how to implement or if this is even a feasible solution for SQLite.
Best, Charlie
