Laurenz Albe <laurenz.albe@xxxxxxxxxxx> writes: > I just tried your commands, and it works as you expect on my PostgreSQL v15 database. It does fail for me, but I think it's a well-known trap rather than a bug (or at least, it's not something that anyone wishes to redesign the rule system to change). The problem is that *a rule is a macro* and therefore it's subject to multiple-evaluation hazards. Your volatile default expression does not play nice with that. Initially you have: insert into "children" values (default); Replacement of the "default" produces: insert into "children" values (gen_random_uuid()); Now the DO ALSO rule produces: insert into "parent" (id) values (gen_random_uuid()); The two insertions will compute different random UUIDs, and kaboom. We tend to recommend using triggers not rules to implement this sort of behavior; they are less prone to surprises. regards, tom lane
