Table: Subject_Selection
Subject Semester Attendee
---------------------------------
ITB001 1 John
ITB001 1 Bob
ITB001 1 Mickey
ITB001 2 Jenny
ITB001 2 James
MKB114 1 John
MKB114 1 Erica
SELECT Subject, Count(*)
FROM Subject_Selection
GROUP BY Subject
Subject Count
------------------------------
ITB001 5
MKB114 2
SELECT Subject, Semester, Count(*)
FROM Subject_Selection
GROUP BY Subject, Semester
Subject Semester Count
------------------------------
ITB001 1 3
ITB001 2 2
MKB114 1 2
原文:https://www.cnblogs.com/WaitSani/p/13194253.html