I would like to delete rows which contain a foreign key, but when I try something like this:
DELETE FROM osoby WHERE id_osoby='1'
I get this statement:
ERROR: update or delete on table "osoby" violates foreign key constraint "kontakty_ibfk_1" on table "kontakty" DETAIL: Key (id_osoby)=(1) is still referenced from table "kontakty".
How can I delete these rows?
To automate this, you could define the foreign key constraint with ON DELETE CASCADE
.
I quote the the manual of foreign key constraints:
CASCADE
specifies that when a referenced row is deleted, row(s) referencing it should be automatically deleted as well.
Look up the current FK definition like this:
SELECT pg_get_constraintdef(oid) AS constraint_def
FROM pg_constraint
WHERE conrelid = 'public.kontakty'::regclass -- assuming pubic schema
AND conname = 'kontakty_ibfk_1';
Then add or modify the ON DELETE ...
part to ON DELETE CASCADE
(preserving everything else as is) in a statement like:
ALTER TABLE kontakty
DROP CONSTRAINT kontakty_ibfk_1
, ADD CONSTRAINT kontakty_ibfk_1
FOREIGN KEY (id_osoby) REFERENCES osoby (id_osoby) ON DELETE CASCADE;
Since there is no ALTER CONSTRAINT
syntax, drop and recreate the constraint in a single ALTER TABLE
statement. That avoids possible race conditions with concurrent write access.
You need the privileges to do so, obviously. The operation takes an ACCESS EXCLUSIVE
lock on table kontakty
and a SHARE ROW EXCLUSIVE
lock on table osoby
.
If you can't ALTER
the table, then deleting by hand (once) or by trigger BEFORE DELETE
(every time) are the remaining options.