Q.Distinguish between a primary key and a foreign key, and explain how a foreign key creates a relationship between two tables with an example.

Both are keys but do opposite jobs — one identifies, the other links. This question asks you to contrast them and show a link.

A primary key and a foreign key are both keys, but they do different jobs.

• A primary key is a field whose value uniquely identifies each record within its own table; it must be unique and never blank.
• A foreign key is a field in one table whose values refer to the primary key of another table. It is the mechanism that creates a relationship (link) between two tables.

Example. Consider two tables:

• Customer(CustID, Name, City) — here CustID is the primary key.
• Orders(OrderNo, CustID, Amount) — here OrderNo is the primary key, and CustID is a foreign key that refers back to CustID in the Customer table. …

A foreign key is not a brand-new special field — it is an ordinary field whose values must match a primary key in another table. Alwa …