"Mysql Index Principle" http://blog.codinglabs.org/articles/theory-of-mysql-index.html
3. 《Mysql inner join left join》
http://justcode.ikeepstudying.com/2016/08/mysql-%E5%9B%BE%E8%A7%A3-inner-join%E3%80%81left-join%E3%80%81right-join%E3%80%81full-outer-join%E3%80%81union%E3%80%81union-all%E7%9A%84%E5%8C%BA%E5%88%AB/
4. 《Mysql MyIsam引擎》http://hudeyong926.iteye.com/blog/1489929