Question

我有一个具有以下结构的表

员工关系表：

| FromEmployeeRelation | ToEmployeeRelation | CreatedAt | UpdatedAt |
+----------------------+--------------------+-----------+-----------+
| 2                    | 3                  | Date      | Date      |

关系表

| Id | EmployeeId | CreatedAt | UpdatedAt |
+----+------------+-----------+-----------+
|2   | 5          | Date      | Date      |
|3   | 7          | Date      | Date      |

来自员工关系表中FromEmployeeRelation和ToEmployeeRelation的外键中的Relation表中的

Id

我正在尝试从员工关系表中获取结果中的实际员工ID信息

结果

| FromEmployeeId | ToEmployeeId | FromEmployeeRelation | ToEmployeeRelation  
+----------------+--------------+----------------------+-------------------
| 5              | 7            | 2                    | 3

从加入我可以从一个关系获得EmployeeId，但我不知道如何获得两个关系的员工ID。

如何做到这一点？感谢

Answer 1

试试这个：

 select e1.EmployeeId  as FromEmployeeId ,
       e2.EmployeeId as ToEmployeeId ,
       er.FromEmployeeRelation,
       er.ToEmployeeRelation
 from emp_relation er
 inner join emp e1 on er.FromEmployeeRelation=e1.id
 inner join emp e2 on er.ToEmployeeRelation=e2.id

SQL小提琴：http://sqlfiddle.com/#!9/ebffe/2

Answer 2

选项1：在两个不同的列SQL Fiddle

上加入单个表

SELECT 
from_tbl.EmployeeId AS FromEmployeeId, 
to_tbl.EmployeeId AS ToEmployeeId, 
e.FromEmployeeRelation, 
e.ToEmployeeRelation
FROM EmployeeRelation e 
INNER JOIN Relation from_tbl ON e.FromEmployeeRelation = from_tbl.Id 
INNER JOIN Relation to_tbl ON e.ToEmployeeRelation = to_tbl.Id

选项2：使用子查询SQL Fiddle

SELECT 
(SELECT from_tbl.EmployeeId FROM Relation from_tbl WHERE e.FromEmployeeRelation = from_tbl.Id) AS FromEmployeeId, 
(SELECT to_tbl.EmployeeId FROM Relation to_tbl WHERE e.ToEmployeeRelation = to_tbl.Id) AS ToEmployeeId, 
e.FromEmployeeRelation, 
e.ToEmployeeRelation
FROM EmployeeRelation e

在SQL

2 个答案: