(id, month) is the primary key of this table. The table has information about the revenue of each department per month. The month has values in ["Jan","Feb","Mar ...

Sometimes primary keys are obvious, for example ... table is Staff ID. A foreign key is a primary key from one table that appears in another table to link the two together. The Department ID ...

(id, month) is the primary key of this table. The table has information about the revenue of each department per month. The month has values in ["Jan","Feb","Mar ...