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PHP

Posted by Priscilla Kam
Priscilla Kam
1,086 Points

mysql - foreign key

what is foreign key in mysql and cascade delete in mysql, and how to use it , does anyone have any example code? Thank you.

1 Answer

Mike Healy
Mike Healy
2,451 Points
Mike Healy
Mike Healy
2,451 Points

When you have a one-to-many relationship in your data the parent row in one table might be linked to its children in another table. For example customers -> orders. A given customer might have made any number of orders.

So the customers table might have an id field The orders table would have a customer_id field which matches the records to the parent.

A foreign key means MySQL is aware of the relationship and orders.customer_id is a foreign key to customers.id

Cascade delete is option that means if the parent row is deleted (the customer) all the related records in the orders table would be deleted too (to prevent orphaned rows).

You could build this logic into your application, but it's usually better and more reliable to have the DB handle it where possible. I'm rusty on the syntax sorry.