PostgreSQL drop constraint with unknown name

Question

I have an SQL script that needs to drop several constraints and restore them at the end, but the constraint names are auto-generated and will be different each time the scri

Answer 1

To dynamically drop & recreate a foreign key constraint, you could wrap it all in a function or use the DO command:

DO
$body$
DECLARE
   _con text := (
      SELECT quote_ident(conname)
      FROM   pg_constraint
      WHERE  conrelid = 'myschema.mytable'::regclass
      AND    confrelid = 'myschema.myreftable'::regclass
      LIMIT 1 -- there could be multiple fk constraints. Deal with it ...
      );

BEGIN
   EXECUTE '
      ALTER TABLE wuchtel12.bet DROP CONSTRAINT ' || _con;

   -- do stuff here

   EXECUTE '
      ALTER TABLE myschema.mytable
      ADD CONSTRAINT ' || _con || ' FOREIGN KEY (col)
      REFERENCES myschema.myreftable (col)';
END
$body$

You must own the table to use ALTER TABLE.
Else you can create a function with LANGUAGE plpgsql SECURITY DEFINER (using the same body) and

ALTER FUNCTION foo() OWNER TO postgres;

postgres being a superuser here - or the owner of the table.
But be sure to know what the manual has to say about security.

The manual also has more on dynamic commands.