Fastest query to see if it returns at least one row

Question

I just need to know if a query returns or not a record.

Of course I can do this:

SELECT COUNT(*) FROM tbl WHERE conds;

But this returns the exact number of rows (of course), and I don't need this overhead.

So I thought this query:

SELECT COUNT(*) FROM (SELECT id FROM tbl WHERE conds LIMIT 1) as t1

Limiting the internal query to 1.

Is this faster? Or considering I am doing a subquery it cancels the benefits of LIMIT 1?

Note: for everyone asking theirself, I can't apply LIMIT 1 to the first query because it doens't work

Answer 1

The inner-select in the second query is redundant.
If you just want to check at-least of one row :-

SELECT 1 FROM tbl  // return 1
WHERE conds        // depends on your index and query
ORDER BY NULL      // avoid file-sort
LIMIT 1;           // minimum row

Answer 2

Why not just:

SELECT 1 FROM tbl WHERE conds LIMIT 1