secondary index
A type of InnoDB index that represents a subset of table columns. An InnoDB table can have zero, one, or many secondary indexes. (Contrast with the clustered index, which is required for each InnoDB table, and stores the data for all the table columns.)
A secondary index can be used to satisfy queries that only require values from the indexed columns. For more complex queries, it can be used to identify the relevant rows in the table, which are then retrieved through lookups using the clustered index.
Creating and dropping secondary indexes has traditionally involved significant overhead from copying all the data in the InnoDB table. The fast index creation feature of the InnoDB Plugin makes both CREATE INDEX and DROP INDEX statements much faster for InnoDB secondary indexes.
See also clustered index.
See also Fast Index Creation.
See also index.