SQL JOIN + COUNT查詢

Question

我試圖顯示一個表格顯示課程列表。我想列出一個欄目，顯示已完成課程的人數，如果可能的話，還包括尚未完成課程的人數。

我的表結構如下所示：

Courses 
courseid | title | etc 

Studying 
courseid | studentid | some other fields | has_completed 

理想的情況下，輸出應該是這樣的，例如：

Course Title | some other fields | Students completed | Students not completed 
Something  etc     5     3 

我有困難得到統計的兩個獨立的領域。任何人都可以推薦一個好方法來做到這一點？

任何意見讚賞，謝謝。

Answer 1

像這樣的東西應該做的：

SELECT c.CourseID, c.Title, SUM(s.Has_Completed) Completed, SUM(1-s.Has_Completed) NotCompleted 
FROM Courses c 
LEFT JOIN Studying s ON c.CourseID = s.CourseID 
GROUP BY c.CourseID, c.Title 

Answer 2

嘗試使用SQL count command

SELECT COUNT(has_completed) FROM Studying WHERE has_completed='1' 

Answer 3

如果HAS_COMPLETED的值爲1爲假的真和0，就可以解決這個問題很簡單：

SELECT c.title, SUM(s.has_completed) as completed, COUNT(studentid) - SUM(s.has_completed) as notCompleted 
FROM Courses c, Studying s 
where c.courseid = s.courseid 
GROUP BY c.courseid, c.title