ALTER TABLE vn.country 
    MODIFY COLUMN code varchar(2) NOT NULL;

ALTER TABLE vn.country 
    ADD CONSTRAINT country_unique UNIQUE KEY (code);

ALTER TABLE vn.transitoryDuaUnified 
    ADD countryCodeFk varchar(2) DEFAULT 'EC' NOT NULL;

ALTER TABLE vn.transitoryDuaUnified 
    ADD CONSTRAINT transitoryDuaUnified_country_FK FOREIGN KEY (countryCodeFk) 
        REFERENCES vn.country(code);
