Take this MySQL performance quiz.
MySQL Query and index optimization are the first and most important task of MySQL performance. Every task can be achieved by several different ways with various queries. However, by knowing the MySQL queries parts limits and drawbacks you can make your MySQL queries perform better.
Join decomposition is a process of decomposing a join: running its single table queries parts and then composing the results at the application side. Can join decomposition give a significant performance boost or is it wasteful?