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(平衡多路搜索樹)
    B-Treey優(yōu)點(diǎn):
    * 磁盤磁頭讀寫移動次數(shù)少,與比較二叉樹，深度較低，葉子節(jié)點(diǎn)存儲數(shù)據(jù)，
2. R-Tree(Rectangle['r?kt??ɡl]  Tree)
3. HASH(main menmory)
4. FULLTEXT(全文索引）

Reference

How MySQL Uses Indexes
Clustered and Secondary Indexes