Does MYSQL join before LIMIT? Imagine that I want to populate the last 10 questions of stackoverflow. I have a table that keep the questions list, a table to keep the question info, a table to list question's asker. 

Now imagine that I want to get the last ten questions, so I have to join some tables and get the last items by ORDER BY ... DESC LIMIT 0 , 10. This gets me the last ten questions without any problems, but I think that there may be one issue.

MySQL may be first joining all tables and then pick the last ten items, so if I have to join 1 million rows to 1 million rows, it gets really bad performance. 

I want to know if MySQL does do this, and if yes, how can I go around this issue?.
The only way around it is to refactor the query so as to alter the order of the EXPLAIN plan.
EXAMPLE : On May 16, 2011, I once answered a very rough question on StackOverflow
Fetching a Single Row from Join Table

Question : I had to join tables together and return only the 40 most recent results.
My Answer : I proved that you can do a JOIN on tables with large rows and get results fast.
How I did it : I had applied principles of refactoring queries I learned from a Youtube Video.

Basically, you have to construct the query so that JOIN clauses are done last. Consequently, this implies that you must get the LIMIT executed beforehand.