MySQL supports various different implementations of fundamental Index Techniques based on the different available Storage Engines. These include:
BTREE
This is the most common index implementation used by the majority of storage engines including MyISAM and InnoDB storage engines.
The InnoDB storage engine supports a clustered primary key B-Tree index. The Tokutek storage engine also supports via their Fractal Tree technology cluster indexes for all indexes.
More Information
- B-Tree description via Wikipedia.
HASH
The HASH index is the default for the Memory Storage Engine.
More Information
- Hash tree description from Wikipedia.
- MySQL Reference Manual – Memory Storage Engine
RTREE
The MyISAM storage engines support spatial indexes via a RTREE index.
More Information
- R-Tree via Wikipedia
- Reference Manual – Creating Spatial Indexes
