mysql相关学习

1. btree索引和hash索引的区别：https://blog.csdn.net/lovezhaohaimig/article/details/80303613

2. Mysql 四种隔离级别：https://www.cnblogs.com/myseries/p/10748912.html

3. 常见的sql优化：https://www.cnblogs.com/kunyun/p/10697040.html

4. limit优化：https://www.iteye.com/blog/uule-2422189