Since MySQL uses BTREE by default when creating an index, is there some instance when I can use HASH? For example, if my table only consists of Foreign Keys which are just INT UNSIGNED values. Is it a good improvement to override BTREE with HASH in this case?
Not sure if it matters, but I'm using InnoDB.
The HASH index type is only supported for MEMORY (aka HEAP) storage engine.
来源：https://stackoverflow.com/questions/14418260/mysql-when-can-i-use-hash-instead-of-btree