Question

If I have two tables tableinfo and tablenamelist and a foreign key like so:

Alter tableinfo add foreign key (name) references tablenamelist(name) on update cascade;

In which situations will the records be modified?

My understanding is that if I change ‘bob’ to ‘Bobby’ in tablenamelist it will update all instances of ‘bob’ to ‘Bobby’ in tableinfo.
What happens though if I change a name in the tableinfo table? If I change a record from ‘bob’ to ‘tim’ will it change records in tableinfo? Or will it just reassign that record to the new name?

Answer 1

Your first assumption is correct, if you change the name in tablenamelist, it will change in table tableinfo.

Your second assumption is incorrect, you will receive a foreign key violation if you try to change the name in table tableinfo to something that does not exist in table tablenamelist.

The foreign key is a constraint that enforces the existance of the key in the foreign table.

From Foreign key

In the context of relational databases, a foreign key is a referential
constraint between two tables.

Also from 14.3.5.4. FOREIGN KEY Constraints

InnoDB rejects any INSERT or UPDATE operation that attempts to create
a foreign key value in a child table if there is no a matching
candidate key value in the parent table.