我目前正在使用 C# 创建一个应用程序,但我在连接两个表时遇到了一些困难。为了让事情更清楚,这里是我的表结构
表1(员工名单)
| EmployeeID | EmployeeName |
+------------+--------------+
| 1 | John Smith |
| 2 | Ian Smosh |
表2(推荐名单)
| PersonalID | InviterID | InterviewerID |
+------------+-----------+---------------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
Datagridview 的输出应该是
| Employee Name | Invites | Interviews |
+---------------+---------+------------+
| John Smith | 2 | 1 |
| Ian Smosh | 0 | 1 |
我目前可以同时获得邀请,但无法同时获得面试。我只能得到一个。
这是我得到的
| Employee Name | Invites |
+---------------+---------+
| John Smith | 2 |
| Ian Smosh | 0 |
这是我的代码:
SELECT Table1.RecruiterName AS Name,
COUNT(Table2.InviterID) AS Invites,
COUNT(Table2.InterviewID) AS Interviews
FROM Table2 LEFT JOIN Table1 ON Table2.InviterID = Table1.EmployeeID
AND Table2.InterviewerID = Table1.InviterID
GROUP BY EmployeeName
有人知道我的代码有什么问题吗?
更新:我设法让它变得更好一点,但我一直在进步
| Employee Name | Invites | Interviews |
+---------------+---------+------------+
| John Smith | 2 | 2 |
| Ian Smosh | 0 | 1 |
John Smith 的条目只有 2 个邀请和 1 个面试。这是我当前的代码
SELECT Recruiters.RecruiterName AS Name, COUNT(Source.SourceID) AS Source, COUNT(Interview.InterviewID) AS Interview
FROM Recruiters
LEFT JOIN Hires Source ON Source.SourceID=Recruiters.RecruiterID
LEFT JOIN Hires Interview ON Interview.InterviewID=Recruiters.RecruiterID
GROUP BY RecruiterName
为什么 John Smith 在采访中得到的金额是错误的,而 Ian Smosh 是正确的。
最佳答案
double join就是double dipping
这应该可以工作
select employee.EmployeeName, inv.count, int.count
from employee
join ( select InviterID,
count(*) as count
from referral
group by InviterID ) as inv
on employee.employeeID = inv.InviterID
join ( select InterviewerID,
count(*) as count
from referral
group by InterviewerID ) as int
on employee.employeeID = int.InterviewerID
关于sql - 连接两个表的问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32176038/