BEGIN;
alter table messaging add column learn varchar(3);
update messaging set learn = 'no' where learn is NULL;
alter table messaging alter column learn set default 'no';
alter table messaging alter column learn set NOT NULL;
alter table messaging add constraint messaging_learn_check CHECK (learn IN ('yes', 'no'));
COMMIT;

alter table messaging drop column target;

BEGIN;
alter table messaging add column defgroup varchar(24);
update messaging set defgroup = '' where defgroup is NULL;
alter table messaging alter column defgroup set default '';
alter table messaging alter column learn set NOT NULL;
COMMIT;
