Re: [GENERAL] ALTER TABLE to add Foreign Key Constraint

[Robert B. Easter]

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