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【DM版本】:0x7000d
【操作系统】：centos
【CPU】:R7 7840HS
【问题描述】*：

现有两张表
1.sys_student
字段:student_id、stu_json、school_id(虚拟列，由stu_json解析得来)...
索引:school_id
2.sys_school
字段:school_id、school_name...
主键索引:school_id

问题:实体字段和虚拟字段的索引是否在关联查询有较大区别，从而影响效率？

几个sql效率有区别，具体如下:

1. 执行耗时：2730ms
   SELECT
   stu.school_id
   FROM
   sys_student stu
   INNER JOIN sys_school sch ON stu.school_id = sch.school_id
   WHERE
   stu.school_id = 2003023234015036573
   执行计划
   

2. 执行耗时3ms
   SELECT
   stu.school_id
   FROM
   sys_student stu
   INNER JOIN sys_school sch ON stu.school_id = sch.school_id
   WHERE
   stu.school_id = 2003023234015036573
   and sch.school_id = 2003023234015036573
   执行计划
   

3. 新增reality_school_id字段，为实体列，值与school_id相同，x新增reality_school_id字段索引
   执行耗时3ms
   select
   stu.school_id as school_id
   from
   sys_student stu
   inner join sys_school sch on stu.reality_school_id = sch.school_id
   where
   stu.reality_school_id = 2003023234015036573
   执行计划