SQL查詢GROUP BY和SUM

Question

我有2個表tblProjects & tblTask​​s

tblProjects已經

ID,PName columns 

tbltasks已經

ID,PID,TaskDescription,Owner,Status 

我想寫一個查詢得到一個狀態其中有多少任務處於所有項目的開啓和關閉狀態

輸出像

PName|Open|Closed 

我使用了一些子查詢和點心和GROUPBY，但並沒有如預期的輸出。

請求專家幫忙。

在此先感謝。 :)

Answer 1

may be this one help 

SELECT t1.ID, 
     t1.PName, 
     Open=SUM(CASE (t2.Status) WHEN 'open' THEN 1 ELSE 0 END), 
     Closed=SUM(CASE (t2.Status) WHEN 'closed' THEN 1 ELSE 0 END) 
FROM tblProjects t1 
INNER JOIN tblTasks t2 
    ON t1.ID = t2.PID 
GROUP BY t1.ID, 
     t1.PName 

Answer 2

我不是專家，但你可以嘗試它使用條件聚合以下簡單查詢：

SELECT t1.ID, 
     t1.PName, 
     SUM(CASE WHEN t2.Status = 'open' THEN 1 ELSE 0 END) AS Open, 
     SUM(CASE WHEN t2.Status = 'closed' THEN 1 ELSE 0 END) AS Closed 
FROM tblProjects t1 
INNER JOIN tblTasks t2 
    ON t1.ID = t2.PID 
GROUP BY t1.ID, 
     t1.PName