What are the data structures used for indexing in MySQL?

There are several main types of data structures used for indexing in MySQL.

1. B-tree index: B-tree index is the most commonly used indexing data structure in MySQL, including B+ tree, B-tree, and B* tree. They are all multi-way search trees that can efficiently support range queries and sorting operations.
2. Hash Index: A hash index uses a hash function to map index values to slots in a hash table, where each slot points to a data record. Hash indexes are suitable for equality queries but not for range queries.
3. Full-text index: Full-text index is primarily used for searching text-based data such as articles, news, etc. In MySQL, full-text index utilizes inverted index to efficiently carry out keyword searches.
4. Spatial index: Spatial index is used for storing data with spatial attributes, such as geographic information data. In MySQL, spatial indexes use data structures like R-tree or R*-tree to support spatial range queries and nearest neighbor searches.

In addition to the common index data structures mentioned above, MySQL also supports other special types of indexes such as prefix indexes, multi-column indexes, unique indexes, and primary key indexes. Choosing the appropriate index type based on specific business needs and query patterns can improve query performance.