MySQL索引原理及慢查询优化

发现排序之前居然锁定了778878条记录，如果针对70万的结果集排序，将是灾难性的，怪不得这么慢，那我们能不能换个思路，先根据contact的created_time排序，再来join会不会比较快呢？

于是改造成下面的语句，也可以用straight_join来优化

select

c.id,

c.name,

c.position,

c.sex,

c.phone,

c.office_phone,

c.feature_info,

c.birthday,

c.creator_id,

c.is_keyperson,

c.giveup_reason,

c.status,

c.data_source,

from_unixtime(c.created_time) as created_time,

from_unixtime(c.last_modified) as last_modified,

c.last_modified_user_id

from

contact c

where

exists (

select

1

from

contact_branch cb

inner join

branch_user bu

on cb.branch_id = bu.branch_id

and bu.status in (

1,

2)

inner join

org_emp_info oei

on oei.data_id = bu.user_id

and oei.node_left >= 2875

and oei.node_right <= 10802

and oei.org_category = - 1

where

c.id = cb.contact_id

)

order by

c.created_time desc limit 0 ,

10;

验证一下效果 预计在1ms内，提升了13000多倍！

10 rows in set (0.00 sec)

（编辑：云计算网_泰州站长网）

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