On 2019-04-04 11:42, Amit Langote wrote: > Hmm, I'm afraid we might get bug reports if we go with this. Why is it OK > to get null in this case when a user explicitly asked for 'foo'?
The way stored generated columns work on foreign tables is that the to-be-stored value is computed, then given to the foreign table handler, which then has to store it, and then return it later when queried. However, since the backing store of a foreign table is typically modifiable directly by the user via other channels, it's possible to create situations where actually stored data does not satisfy the generation expression. That is the case here. I don't know of a principled way to prevent that. It's just one of the problems that can happen when you store data in a foreign table: You have very little control over what data actually ends up being stored. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
