在排查所有查询语句效率的过程中 , 发现了join关联表的时候 , 被驱动表没有走索引而是进行的全表扫描 实际的sql语句如下: explain select a.* from audit_rules a left join audit_rules_detail b on a.id=b.rule_id where a.ent_id=23684 输出: +----+-------------+-------+------+---------------+------------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------------+---------+-------+------+-------+ | 1 | SIMPLE | a | ref | idx_ent_id | idx_ent_id | 4 | const | 12 | | | 1 | SIMPLE | b | ALL | NULL | NULL | NULL | NULL | 35 | | +----+-------------+-------+------+---------------+------------+---------+-------+------+-------+ 看到表b是全表扫描 , 这是因为b的字段rule_id没有索引 增加上索引以后 +----+-------------+-------+------+---------------+-------------+---------+--------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+-------------+---------+--------------+------+-------------+ | 1 | SIMPLE | a | ref | idx_ent_id | idx_ent_id | 4 | const | 12 | | | 1 | SIMPLE | b | ref | idx_rule_id | idx_rule_id | 4 | sinanet.a.id | 1 | Using index | MySQL是只支持一种JOIN算法Nested-Loop Join(嵌套循环链接) 没有索引时:
有索引时
|
|