Does it make sense to do an INDEX on a foreign key if the parent table has only 10-1000 records?

Question

MySQL

The parent table has a primary key of type TINYINT UNSIGNED or SMALLINT UNSIGNED.

Answer 1

Of course you do. And in general, you need to accustom yourself to search only for those fields on which the index is built. This is a good practice rule. Of course, either action or inaction will not affect performance or disk space, but in order to discipline yourself, this is necessary. This is my opinion based on life experience.

Answer 2

Surely, your requests will be fulfilled much faster.
You make indexes, foreign keys and selects on them later