Re: ALTER TABLE to add Foreign Key Constraint

On Sat, 17 Jun 2000, Vipin Samtani wrote:
> I am trying to designate foreign keys after tables "distributors" and
> "addresses" have already been created with primary keys "distributor"
> and "address" respectively. I am attempting to use ALTER TABLE to
> accomplish this. I found this statement in the documentation
>
> ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address)
> REFERENCES addresses(address) MATCH FULL
>
>
> When I run it, I get this error:
>
> ERROR: parser: parse error at or near "constraint"
>
> What is wrong with the statement?

Consider this example:

-- Load the PGSQL procedural language
-- This could also be done with the createlang script/program.
-- See man createlang.
CREATE FUNCTION plpgsql_call_handler()
RETURNS OPAQUE AS '/usr/local/pgsql/lib/plpgsql.so'
LANGUAGE 'C';
CREATE TRUSTED PROCEDURAL LANGUAGE 'plpgsql'
HANDLER plpgsql_call_handler
LANCOMPILER 'PL/pgSQL';

CREATE TABLE test1 (id INTEGER PRIMARY KEY);
CREATE TABLE test2 (id INTEGER PRIMARY KEY);

ALTER TABLE test1 ADD CONSTRAINT test1_id_fk
FOREIGN KEY (id) REFERENCES test2
ON UPDATE CASCADE
ON DELETE CASCADE -- can delete test2
INITIALLY DEFERRED;
ALTER TABLE test2 ADD CONSTRAINT test1_id_fk
FOREIGN KEY (id) REFERENCES test1
ON UPDATE CASCADE
ON DELETE RESTRICT -- disallows delete test1
INITIALLY DEFERRED;

CREATE SEQUENCE test_id_seq;

CREATE FUNCTION new_tests() RETURNS INTEGER AS '
DECLARE
new_seq INTEGER;
BEGIN
new_seq := nextval(''test_id_seq'');
INSERT INTO test1 VALUES (new_seq);
INSERT INTO test2 VALUES (new_seq);
RETURN new_seq;
END;
' LANGUAGE 'plpgsql';

-- implicit BEGIN;
SELECT new_tests();
-- implicit COMMIT;
SELECT new_tests();
SELECT new_tests();

SELECT * FROM test1;
SELECT * FROM test2;

DELETE FROM test1 WHERE id = 1; -- this will fail
DELETE FROM test2 WHERE id = 1; -- this will succeed and cacade

SELECT * FROM test1;
SELECT * FROM test2;

--
Robert B. Easter