Answers for "psql how to put foreign keys in tables"

postgres add foreign key to existing table

ALTER TABLE tblA ADD COLUMN colA VARCHAR(10); /* 1st add column */
ALTER TABLE tblA ADD CONSTRAINT colA /* Make colA on tblA a foreign key */
FOREIGN KEY (colA) REFERENCES tblB (colB); /* colB must be a pk on tblB*/

postgre alter table foreign key

ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) MATCH FULL;