On Wed, Feb 03, 2021 at 08:35:41AM -0700, David G. Johnston wrote: > On Wed, Feb 3, 2021 at 8:23 AM Mai Peng <[1]maily.peng@xxxxxxxxxxxxxxxxx> wrote: > > Hello, > > I’ve got a table name publication, and another table named publication_item. > Each publication_item is linked to a publication by publication_id. > How could I add a constraint that check each publication has one or more publication_item when a tuple is inserted ? > I don’t want to store items in the same table as publication because we could have 1-> n items. > > [2]https://www.postgresql.org/docs/current/tutorial-fk.html I don't think it helps. Fkey can check that publication_item contains valid publication_id, but doesn't ensure that every publication has at least one item. As for the problem of OP, I think this describes working solution: https://www.depesz.com/2017/07/03/how-to-make-sure-there-is-always-at-least-one-sub-record/ Best regards, depesz
