Does using “LIMIT 1” speed up a query on a primary key?

Question

If I have a primary key of say id and I do a simple query for the key such as,

SELECT id FROM myTable WHERE id = X

Will it find on

Answer 1

Does using “LIMIT 1” speed up a query on a primary key?

No. It's already as fast as can be without LIMIT 1. LIMIT 1 is effectively implied anyway.

Will it find one row and then stop looking as it is a primary key

Yes.

No table scan should be necessary at all here: it's a key-based lookup. The matching row is found and that's the end of the procedure.