Optimizing SELECT statements

SELECT statements perform all the lookup operations in the database, so tuning them is a top priority, and the same techniques apply to CREATE TABLE...AS SELECT, INSERT INTO...SELECT, and WHERE clauses in DELETE statements. To make a slow SELECT ... WHERE query faster, the first thing to check is whether you can add an index: index the columns used in the WHERE clause to speed evaluation, filtering, and row retrieval, but build a small set of indexes that speeds many related queries. Indexes matter most for queries that reference different tables through joins and foreign keys, and EXPLAIN shows which indexes a SELECT uses. Isolate and tune any part of the query, such as a function call, that takes excessive time, and minimize full table scans on big tables. Run ANALYZE TABLE periodically so the optimizer has current statistics for efficient plans, learn the tuning techniques specific to each table's storage engine, and size memory areas such as the InnoDB buffer pool. If a problem persists, read the EXPLAIN plan and adjust indexes, WHERE clauses, and join clauses. Scope: MySQL 8.4. Reviewed October 4, 2026.