hash index
A type of index intended for queries that use equality operators, rather than range operators such as greater-than or BETWEEN. It is available in only the MEMORY storage engine. Although hash indexes are the default for MEMORY tables for historic reasons, that storage engine also supports B-tree indexes, which are often a better choice for general-purpose queries.
The InnoDB storage engine includes a variant of this index type, the adaptive hash index, that is constructed automatically if needed based on runtime conditions.
See also adaptive hash index.
See also B-tree.
See also index.