Re: Problem with some keys

The "ON UPDATE SET DEFAULT" clause in the FK definition tells Postgres
to change the value of mostra.museo to the default value of
museo.nomemuseo, which is 'MuseoVeronese'. In other words, it is as if
you had executed this:

UPDATE mostra SET museo = 'MuseoVeronese';

If you execute the statement above, you will see the same error. The
error is telling you that there is no row in the museo table with a
nomemuseo value of 'MuseoVeronese', so the FK relationship from mostra
to museo is violated. Looking at your INSERT statements, I see that you
never created a row for that museum; if you insert a row for
'MuseoVeronese' in museo, your problem will go away.

--
Peter Headland