Explain different types of keys in a database.

Primary Key: Uniquely identifies each row in a table

• Cannot be NULL
• Must be unique
• Example: CustomerID in Customer table

Foreign Key: References primary key of another table

• Establishes relationships between tables
• Can be NULL (unless constrained)
• Example: CustomerID in Order table referencing Customer table

Candidate Key: Any column or combination that could serve as primary key

• Unique and not NULL
• A table can have multiple candidate keys

Composite Key: Primary key made up of multiple columns

• Example: (OrderID, ProductID) in OrderDetails table

Unique Key: Ensures uniqueness but allows one NULL value

• Similar to primary key but allows NULL

Super Key: Any combination of columns that uniquely identifies a row

• Includes primary key and additional columns