sql - Best way to test if a row exists in a MySQL table

Question

I'm trying to find out if a row exists in a table. Using MySQL, is it better to do a query like this:

SELECT COUNT(*) AS total FROM table1 WHERE ...

and check to see if the total is non-zero or is it better to do a query like this:

SELECT * FROM table1 WHERE ... LIMIT 1

and check to see if any rows were returned?

In both queries, the WHERE clause uses an index.

Answer 1

You could also try EXISTS:

SELECT EXISTS(SELECT * FROM table1 WHERE ...)

and per the documentation, you can SELECT anything.

Traditionally, an EXISTS subquery starts with SELECT *, but it could begin with SELECT 5 or SELECT column1 or anything at all. MySQL ignores the SELECT list in such a subquery, so it makes no difference.