MySQL - SELECT WHERE field IN (subquery) - Extremely slow why?

Question

I\'ve got a couple of duplicates in a database that I want to inspect, so what I did to see which are duplicates, I did this:

SELECT relevant_field
FROM some         


        

Answer 1

Subqueries vs joins

http://www.scribd.com/doc/2546837/New-Subquery-Optimizations-In-MySQL-6