MySQL Cannot Add Foreign Key Constraint

Question

So I\'m trying to add Foreign Key constraints to my database as a project requirement and it worked the first time or two on different tables, but I have two tables on which

Answer 1

Confirm that the character encoding and collation for the two tables is the same.

In my own case, one of the tables was using utf8 and the other was using latin1.

I had another case where the encoding was the same but the collation different. One utf8_general_ci the other utf8_unicode_ci

You can run this command to set the encoding and collation for a table.

ALTER TABLE tablename CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;

I hope this helps someone.