What are some examples of foreign key constraints in databases?

What are some examples of foreign key constraints in databases?

Foreign key constraints are rules that maintain referential integrity between tables. For example, in a database with a 'Customers' table and an 'Orders' table, the 'Orders' table can have a foreign key that references the 'CustomerID' in the 'Customers' table. This ensures that every order is linked to a valid customer.

Can you give me another example?

Sure! Consider a 'Students' table and a 'Courses' table. The 'Courses' table can have a foreign key that references 'StudentID' in the 'Students' table, ensuring that each course enrollment is associated with a valid student.

What happens if a foreign key constraint is violated?

If a foreign key constraint is violated, the database will prevent the operation that caused the violation, such as inserting an order for a non-existent customer. This helps maintain data integrity.

How can I create a foreign key constraint in SQL?

You can create a foreign key constraint in SQL using the following syntax: ALTER TABLE Orders ADD CONSTRAINT fk_customer FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID); This links the 'CustomerID' in 'Orders' to the 'CustomerID' in 'Customers'.