A foreign key constraint enforces referential integrity by linking a column in one table to the primary key of another table.

Explanation:

• Ensures valid relationships between tables.
• Prevents deleting referenced data unless cascading rules are set.

Example SQL Foreign Key Constraint:

sqlCopyEditCREATE TABLE Employees (
    emp_id INT PRIMARY KEY,
    dept_id INT,
    FOREIGN KEY (dept_id) REFERENCES Departments(dept_id) ON DELETE SET NULL
);

Here, if a department is deleted, dept_id in Employees will be set to NULL instead of being removed.