A foreign key is a field in one table that uniquely identifies a row in another table, linking to the primary key of that table.
For example, DepartmentID in the Employees table links to DepartmentID in the Departments table.
Foreign keys establish relationships between tables and maintain referential integrity by ensuring valid connections between records.
Departments Table
| DepartmentID | DepartmentName |
|---|---|
| 1 | Human Resources |
| 2 | IT |
| 3 | Marketing |
Employees Table
| EmployeeID | EmployeeName | DepartmentID |
|---|---|---|
| 101 | Alice | 1 |
| 102 | Bob | 2 |
| 103 | Charlie | 1 |
| 104 | Dana | 3 |