Q:The kind of mysql index
1.Primary Key
2.Unique index
3.Normal index
4.Fulltext index
5.Clustered index
Every InnoDB table has a special index called the clustered index where the data for the rows is stored.
When you define a PRIMARY KEY on your table, InnoDB uses it as the clustered index.
6.Secondary index
All indexes other than the clustered index are known as secondary indexes.
Q:The implement method of the index
1. B-Tree(平衡多路搜索树)
B-Treey优点:
* 磁盘磁头读写移动次数少,与比较二叉树，深度较低，叶子节点存储数据，
2. R-Tree(Rectangle['rɛktæŋɡl] Tree)
3. HASH(main menmory)
4. FULLTEXT(全文索引）
Reference
How MySQL Uses Indexes
Clustered and Secondary Indexes
