子查询优化

最新推荐文章于 2024-10-04 01:47:47 发布

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最新推荐文章于 2024-10-04 01:47:47 发布

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本文通过两个具体的SQL查询案例，展示了如何从多个关联表中筛选特定条件的数据，并针对登录ID为'2101'的用户进行相关信息的提取。通过对比两种不同的查询方式，深入剖析了SQL查询语句的构造及优化思路。

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 --action1 1.297 seconds
 select cm.customerid from 
 zx_dm_customer_manage cm ,
 (
      select t.customid from 
      zx_dm_employee_customer t,
      (
                    select t.employeeid from 
                    user_employee t,
                    (select t.id FROM users t where t.loginid='2101') t_userid_A
                    where t.userid=t_userid_A.id
      ) t_employeeid_B where t.employeeid=t_employeeid_B.employeeid
 ) t_customerid_C
 where cm.customerid in t_customerid_C.customid and cm.ifsellnote=1
 
 --action2 0.032 seconds
 select cm.customerid from 
 zx_dm_customer_manage cm
 where cm.customerid in 
  (
      select t.customid from 
      zx_dm_employee_customer t,
      (
                    select t.employeeid from 
                    user_employee t,
                    (select t.id FROM users t where t.loginid='2101') t_userid_A
                    where t.userid=t_userid_A.id
      ) t_employeeid_B where t.employeeid=t_employeeid_B.employeeid
 )
 and cm.ifsellnote=1