2 different small query vs 1 query with subquery

Question

I have table like this

name       | personal_number 
-----------------------------------------
Jon        | 222
Alex       | 555
Jon        | 222
Jimmy               


        

Answer 1

It seems that subqueries are very slow as mentioned in this article http://www.mysqlperformanceblog.com/2010/10/25/mysql-limitations-part-3-subqueries.

You should try to avoid having subqueries and use joining instead.