MySQL 8.4 Release Notes
始终检查所有查询是否确实使用了在表中创建的索引。使用 EXPLAIN 语句,如 第 10.8.1 节,“使用 EXPLAIN 优化查询” 中所述。Always check whether all your queries really use the indexes
that you have created in the tables. Use the
EXPLAIN statement, as described
in Section 10.8.1, “Optimizing Queries with EXPLAIN”.