Dangling SSNs in PERSON not referencing INCOME

[ReneNyffenegger]

Although SSN in PERSON is declared as foreign key to INCOME, there are some records in PERSON whose SSNs don't reference the primary key in INCOME. This is possible because SQLite does not enforce foreign keys by default.

sqlite> select count(*) from person where ssn not in (select ssn from income);
2497

This caused quite a bit of mystery when I tried to port the game to another database.

Similarly, there are 5 persons whose LICENSE_ID is not found in DRIVERS_LICENSE:

select * from person where license_id not in (select id from drivers_license);