8.3 Optimization and Indexes

8.3.1 How MySQL Uses Indexes
8.3.2 Using Primary Keys
8.3.3 Using Foreign Keys
8.3.4 Column Indexes
8.3.5 Multiple-Column Indexes
8.3.6 Verifying Index Usage
8.3.7 InnoDB and MyISAM Index Statistics Collection
8.3.8 Comparison of B-Tree and Hash Indexes

The best way to improve the performance of SELECT operations is to create indexes on one or more of the columns that are tested in the query. The index entries act like pointers to the table rows, allowing the query to quickly determine which rows match a condition in the WHERE clause, and retrieve the other column values for those rows. All MySQL data types can be indexed.

Although it can be tempting to create an indexes for every possible column used in a query, unnecessary indexes waste space and waste time for MySQL to determine which indexes to use. You must find the right balance to achieve fast queries using the optimal set of indexes.