Saluton, suppose we have PostgreSQL 7.0.2 and two tables, a and b, like: a: id serial primary key ... b: a int4 not null references a(id) ... In general there will be several rows in b with the same b.a, but how can I make sure there is AT LEAST ONE row referencing a given id from table a? It seems obvious to me that this can only be meaningful in a transaction, like: begin insert into a ...; insert into b (a,...) values (curr_val(a_id_seq),...); commit And the check can only be made before committing. My first idea (which was not very good) was to add a table constraint on table a similar to `... foreign key (a) references b(a) initially deferred', because only a foreign key seems to allow checks to be deferred, and I cannot tell from the docs whether a foreign key is actually incompatible with a primary key declaration on the same field. - Of course this does not work, as there is no table b by the time a is created, or vice versa. Looking at the documentation for CREATE TRIGGER, I do not see how to get it to fire only just before commit - I would need a syntax like create trigger ... before commit insert on a execute ..., which is not what is there. Rules - another one of those exotic things I never thought I might actually need - do not seem to provide a solution, either. As long as I know that nobody will mess around with the database directly but only with scripts I provide, I can easily provide the necessary checks etc., so this may be not so much of an issue really. Still, it would be good to know that this works, and I am pretty sure that this must be possible, but I seem to be looking in the wrong direction. Any help would be appreciated. Thanks in advance, Albert. -- -------------------------------------------------------------------------- Albert Reiner <[EMAIL PROTECTED]> Deutsch * English * Esperanto * Latine --------------------------------------------------------------------------
