SQL多表联系查询

SQL多表联系查询

首先二张表连接查询：A表：EUser  B表：ESchool

一、外连接：左连接、右连接、全然外连接。

左连接：left join 或 left outer join

  select * from EUser left join ESchool  on EUser.SchoolId=ESchool.ScholId 

右连接：right join 或 right outer join

select * from EUser right join ESchool  on EUser.SchoolId=ESchool.ScholId 

全然外连接：  full join 或 full outer join

  select * from EUser full join ESchool  on EUser.SchoolId=ESchool.ScholId 

二、内连接： join 或 inner join

select * from EUser INNER JOIN ESchool  on EUser.SchoolId=ESchool.ScholId 

三张表连接查询：A表：EUser  B表：ESchool  C表：EXibu

方法一：

  select * from EUser INNER JOIN ESchool  on EUser.SchoolId=ESchool.ScholId 
  INNER JOIN EXibu on ESchool.ScholId=EXibu.SchoolId and EUser.DepartmentId=EXibu.DepartmentId

方法二：

  select * from EUser as sc left join ESchool as s on s.ScholId=sc.SchoolId
  left join EXibu as c on c.DepartmentId=sc.DepartmentId

了解内连接与外连接可以：https://www.cnblogs.com/mvpbest/p/13879121.html