Storage engine API for indexes

There are quite a few methods in the handler class that deal with indexes. Luckily, we do not have to implement every single one of them. Still, it is good to know what methods exist and what possibilities we have. The table below lists most of the handler methods related to indexes:

Name	Description
index_type	This is a purely informational method, similar to the table_type() method, and it returns a string with the index type. Often, it is either "HASH" or "BTREE", but it can be just anything. For example, Federated engine returns "REMOTE" here. This method takes an index number as an argument, as different indexes may be of different types.
index_flags	This is, too, similar to the table_flags() method. It returns a bitmap defining index capabilities that, depending on arguments, describe a whole index, a specific key part (one column in a multi-column index), or an index prefix up to and including a given key part. Index capability flags...