MySQL中关联的字段数据类型不一致会导致索引失效-CFANZ编程社区

数据类型不一致会导致索引失效

下面案例中fk_do_depart 是varchar类型的, 如果关联的字段不是varchar类型的话会导致索引失效

用相同的数据类型关联

注意观察 fk_do_depart = ‘10001108’ ,两个都是varchar类型的

EXPLAIN
SELECT do.fk_definition_id, t3.fk_org_region_id
FROM t_user_account t1
         INNER JOIN t_relation_account_role t2 ON t1.pk_account_id = t2.fk_account_Id
         INNER JOIN t_relation_account_organization_region t3 ON t1.pk_account_id = t3.fk_account_id
         INNER JOIN t_approval_do do
                    ON do.fk_do_depart = '10001108' AND do.account_month = '2020-12'
                        AND do.fk_do_role = 12
WHERE t1.ds = 0
  AND t2.ds = 0
  AND t2.fk_role_id = 12
  AND t1.account_state = 1
  AND t3.ds = 0
  AND t3.data_state = 1
  AND t1.mobile = 13688888888;

执行结果:

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	do	ref	idx_definition_depart_role	idx_definition_depart_role	133	const,const	74	Using where; Using index
1	SIMPLE	t1	eq_ref	PRIMARY,UI_ur_tuseraccot	PRIMARY	4	wxapp.t2.fk_account_Id	1	Using where
1	SIMPLE	t2	ref	FK_Reference_19,FK_Reference_4	FK_Reference_4	5	const	1808	Using where
1	SIMPLE	t3	ref	FK_Reference_20	FK_Reference_20	5	wxapp.t2.fk_account_Id	1	Using where

结果可以发现 do这个表 type是 ref , ref是 const,const rows扫描了74行

用不同的数据类型关联

注意观察这个SQL和上面的SQL几乎是一模一样的,只是 fk_do_depart = 10001108 和上面的不一样,fk_do_depart 是varchar类型的, 而后面 10001108是数字

EXPLAIN
SELECT do.fk_definition_id, t3.fk_org_region_id
FROM t_user_account t1
         INNER JOIN t_relation_account_role t2 ON t1.pk_account_id = t2.fk_account_Id
         INNER JOIN t_relation_account_organization_region t3 ON t1.pk_account_id = t3.fk_account_id
         INNER JOIN t_approval_do do
                    ON do.fk_do_depart = 10001108 AND do.account_month = '2020-12'
                        AND do.fk_do_role = 12
WHERE t1.ds = 0
  AND t2.ds = 0
  AND t2.fk_role_id = 12
  AND t1.account_state = 1
  AND t3.ds = 0
  AND t3.data_state = 1
  AND t1.mobile = 13688888888;

执行结果:

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	do	index	idx_definition_depart_role	idx_definition_depart_role	213	NULL	3524	Using where; Using index; Using join buffer (Block Nested Loop)
1	SIMPLE	t1	eq_ref	PRIMARY,UI_ur_tuseraccot	PRIMARY	4	wxapp.t2.fk_account_Id	1	Using where
1	SIMPLE	t2	ref	FK_Reference_19,FK_Reference_4	FK_Reference_4	5	const	1808	Using where
1	SIMPLE	t3	ref	FK_Reference_20	FK_Reference_20	5	wxapp.t2.fk_account_Id	1	Using where