我想在兩個詳細表(StandardCourses
和StandardPosts
)中計數StandardID
。
我寫了這個代碼如何計數子表中的ID?
Select es.StandardID, count(esc.StandardCourseID) as CourseIDCount,
count(esp.StandardPostID) as PostIDCount
from EduStandards as es
left join EduStandardCourses as esc on es.StandardID = esc.StandardID
left join EduStandardPosts as esp on es.StandardID = esp.StandardID
group by es.StandardID
但它返回false結果:
StandardID | CourseID | PostID
-----------+----------+--------
3 | 2 | 2
4 | 1 | 1
5 | 1 | 0
9 | 1 | 0
雖然它必須返回:
StandardID | CourseID | PostID
-----------+----------+--------
3 | 1 | 2
4 | 1 | 1
5 | 1 | 0
9 | 1 | 0