我有三个表像波纹管SQL查询组由case语句
**tRole**
+--------+----------+-----------+
| RoleID | RoleCode | RoleTitle |
+--------+----------+-----------+
| 1 | Role1 | RT1 |
| 2 | Role2 | RT2 |
| 3 | Role3 | RT3 |
+--------+----------+-----------+
**tEmployee**
+-------+-------+
| EmpID | Name |
+-------+-------+
| 1 | Emp 1 |
| 2 | Emp 2 |
| 3 | Emp 3 |
+-------+-------+
**tEmployeeRole**
+-------+--------+
| EmpID | RoleID |
+-------+--------+
| 1 | 1 |
| 1 | 2 |
| 2 | 1 |
| 2 | 2 |
| 3 | 3 |
+-------+--------+
我要像下方的输出,如果一个角色只有一个员工,然后员工姓名映射将显示其他明智的多会展现出来。
+--------+----------+-----------+----------+
| RoleID | RoleCode | RoleTitle | Employee |
+--------+----------+-----------+----------+
| 1 | Role1 | RT1 | Multiple |
| 2 | Role2 | RT2 | Multiple |
| 3 | Role3 | RT3 | Emp 3 |
+--------+----------+-----------+----------+
我写的波纹管查询,但是当我通过emp.First_Name一组,那么结果是错误的
select cr.RoleCode,cr.RoleID,
case
when count(ear.RoleID)=1 then emp.First_Name
else 'M' end as 'AssignedTO'
from tRole as cr
left outer join tEmployeeRole as ear on cr.RoleID=ear.RoleID
left outer join tEmployee as emp on ear.EmployeeID=emp.EmployeeID
group by cr.RoleCode,crRoleID,emp.First_Name