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 one row and then stop looking as it is a primary key, or would it be better to tell mysql to limit its select by using LIMIT 1? For instance:
SELECT id FROM myTable WHERE id = X LIMIT 1
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Answer
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.