BEGIN;
UPDATE game
SET number_of_songs = 0
WHERE number_of_songs IS NULL;
UPDATE game
SET hash = ''
WHERE hash IS NULL;
UPDATE song
SET hash = ''
WHERE hash IS NULL;
COMMIT;
BEGIN;
Alter table game
alter column number_of_songs set not null,
alter column number_of_songs set default 0,
ALTER COLUMN hash SET NOT NULL;
ALTER TABLE song
ALTER COLUMN hash SET NOT NULL;
COMMIT;