Question

我有表活动，会话， sessionspeaker ，发言人和员工事件表 EventID 为 PK ，会话表可以有多个Eventid 并且 sessionid pk ，发言人表格 speakerid 为pk，并且 empID 列，员工 table的 empID 为 PK 。 sessionspeaker 表格（sessionid，speakerid）为pk。 现在我喜欢用Topmost emplID来讨论所有的偶数，以便事件id是唯一的

SELECT     emp.EmployeeID, e.EventID
FROM    Event AS e INNER JOIN Session ON e.EventID = Session.EventID left outer JOIN
SessionSpeaker ON Session.SessionID = SessionSpeaker.SessionID INNER JOIN
Speaker ON SessionSpeaker.EmployeeID = Speaker.EmployeeID INNER JOIN
Employee AS emp ON Speaker.EmployeeID = emp.EmployeeID

此查询返回

EmployeeID   EventID
5351         310
5351         310
5352         299
5352         300
5352         301
5352         302
5352             303
5352         314
5352         315

这是我不想要的，我想要唯一的事件ID和最顶层的employeeID 请告诉我一个解决这个问题的简单方法。将分组，拥有或计算这方面的帮助

Answer 1

我想要唯一的事件ID和最顶层的employeeID

只需GROUP BY e.EventID并选择MAX(EmployeeId)：

SELECT 
  e.EventID, 
  MAX(emp.EmployeeID) AS TopMostEmpId, 
FROM    Event AS e 
INNER JOIN Session         ON e.EventID                 = Session.EventID 
INNER JOIN SessionSpeaker  ON Session.SessionID         = SessionSpeaker.SessionID 
INNER JOIN Speaker         ON SessionSpeaker.EmployeeID = Speaker.EmployeeID 
INNER JOIN Employee AS emp ON Speaker.EmployeeID        = emp.EmployeeID
GROUP BY e.EventID

如果您想要选择的列数多于eventId，employeeId，则可以使用以下排名函数：

WITH CTE AS
(
    SELECT 
      e.EventID, 
      emp.EmployeeID,
      e.EventName,
      emp.EmployeeName,
      ...
      ROW_NUMBER() OVER(PARTITION BY e.EventID 
                        ORDER BY emp.EmployeeId DESC) AS RN
    FROM    Event AS e 
    INNER JOIN Session         ON e.EventID                 = Session.EventID 
    INNER JOIN SessionSpeaker  ON Session.SessionID         = SessionSpeaker.SessionID 
    INNER JOIN Speaker         ON SessionSpeaker.EmployeeID = Speaker.EmployeeID 
    INNER JOIN Employee AS emp ON Speaker.EmployeeID        = emp.EmployeeID
) 
SELECT *
FROM CTE
WHERE RN = 1;

Answer 2

SELECT     emp.EmployeeID, distinct e.EventID
FROM    Event AS e INNER JOIN Session ON e.EventID = Session.EventID left outer JOIN
SessionSpeaker ON Session.SessionID = SessionSpeaker.SessionID INNER JOIN
Speaker ON SessionSpeaker.EmployeeID = Speaker.EmployeeID INNER JOIN
Employee AS emp ON Speaker.EmployeeID = emp.EmployeeID 

group by e.EventID

在加入后从表中获取唯一记录

2 个答案: