From: | Chuck Martin <clmartin(at)theombudsman(dot)com> |
---|---|
To: | pgsql-general <pgsql-general(at)postgresql(dot)org> |
Subject: | INSERT where not exists with foreign key |
Date: | 2019-05-20 18:11:50 |
Message-ID: | CAFw6=U3Nh09ynmu+J950izZtpqRHP4znK1qYbR0meHyMBHyd8A@mail.gmail.com |
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Lists: | pgsql-general |
My Google foo isn't working on this question, probably because I don't
understand the question well enough. I'm using Postgres 11.3 on Centos 7.
I'm trying to insert a record in table A with a foreign key to table B, but
only where there is not already a foreign key in A to B. So assume this
simple structure:
Table A
A.key Integer
A.something text
A.Bkey Integer [foreign key to table B, column B.key
Table B (or View C)
B.key Integer
[more columns]
Thinking that it might simplify matters, I created a view to table B that
only includes records with no foreign key in Table A. But still, after
reading the documentation and Googling, I can't work out what seems like it
should be simple. Among the many things that didn't work is:
INSERT INTO A(something,A.Bkey)
VALUES ('text',
(SELECT C.key FROM C)
But this didn't work because the subquery returned more than one value. Of
course I want it to return all values, but just one per insert.
I can do this outside of Postgres, but would like to learn how to do this
with SQL.
Chuck Martin
Avondale Software
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