MySQL：基於事件類型計數事件出勤

Question

我有三個表設置用於跟蹤參加事件。這些表如下：

Users 
-------- 
rid 
name 

Events 
-------- 
eid 
name 
type (either 0 or 1) 

Attendance 
-------- 
rid 
eid 

我試圖返回的所有用戶，並打印出他們參加過破入量1型和0

事件的數量的計數

我可以成功地返回一個或另一個但不是兩者的用下面的語句組合：

SELECT users.name, COUNT(type) as typeCount FROM attendance, events, users 
WHERE users.rid=attendance.rid && events.eid=attendance.eid && type=1 GROUP BY users.rid 

它返回

╔══════╦══════════════╗ 
║ name ║ typeCount ║ 
╠══════╬══════════════╣ 
║ John ║  5  ║ 
╠══════╬══════════════╣ 
║ Jack ║  3  ║ 
╚══════╩══════════════╝ 

但我想它返回

╔══════╦══════════════╦═════════════╗ 
║ name ║ type0Count ║ type1Count ║ 
╠══════╬══════════════╬═════════════╣ 
║ John ║  2  ║  5  ║ 
╠══════╬══════════════╬═════════════╣ 
║ Jack ║  7  ║  3  ║ 
╚══════╩══════════════╩═════════════╝ 

Answer 1

您可以使用CASE...WHEN的COUNT函數裏面計算列中的特定值。

SELECT 
    Users.rid, 
    Users.Name, 
    COUNT(CASE Events.type WHEN 0 THEN 1 ELSE NULL END) AS type0Count, 
    COUNT(CASE Events.type WHEN 1 THEN 1 ELSE NULL END) AS type1Count 
FROM Users 
INNER JOIN Attendance ON Users.rid = Attendance.rid 
INNER JOIN Events ON Attendance.eid = Events.eid 
GROUP BY Users.rid, Users.Name 

您還可以使用IF或NULLIF爲好。

Answer 2

你必須從過濾器取出型

SELECT users.name,type, COUNT(type) as typeCount 
FROM attendance, events, users 
WHERE 
users.rid=attendance.rid 
&& events.eid=attendance.eid 
GROUP BY users.rid,type 

或

SELECT users.name, 
CASE WHEN type = 0 THEN COUNT(1) AS type0Count END, 
CASE WHEN type = 1 THEN COUNT(1) AS type1Count END 
FROM attendance, events, users 
WHERE users.rid=attendance.rid 
&& 
events.eid=attendance.eid 
GROUP BY users.rid