sql - 如何消除重复sql？

Question

有人可以指出正确的方向以消除学生证字段中的重复项吗？

SQL> select DISTINCT(student_class.student_id) as student_Num,student_class.class_id,
  2  event.event_id, event.event_name
  3  from student_class, event
  4  where student_class.class_id = '10'
  5  and event.class_id = '10';

STUDENT_NUM   CLASS_ID   EVENT_ID EVENT_NAME
----------- ---------- ---------- --------------------------------------------------
         12         10          2 Flag FOOtball Game
         12         10          5 PICKUP SOCCER GAME
          9         10          5 PICKUP SOCCER GAME
         16         10          5 PICKUP SOCCER GAME
          6         10          2 Flag FOOtball Game
         18         10          5 PICKUP SOCCER GAME
          4         10          5 PICKUP SOCCER GAME
          4         10          2 Flag FOOtball Game
         16         10          2 Flag FOOtball Game
         20         10          2 Flag FOOtball Game
          3         10          5 PICKUP SOCCER GAME
          2         10          5 PICKUP SOCCER GAME
          3         10          2 Flag FOOtball Game
          8         10          2 Flag FOOtball Game
          9         10          2 Flag FOOtball Game
          2         10          2 Flag FOOtball Game
          6         10          5 PICKUP SOCCER GAME
         20         10          5 PICKUP SOCCER GAME
         18         10          2 Flag FOOtball Game
          8         10          5 PICKUP SOCCER GAME

Answer 1

尝试SQL>

  SELECT DISTINCT event.event_id,event.event_name,COUNT(student_class.student_id) AS 'Total Students'
   FROM student_class, event
   WHERE student_class.class_id = '10'
   AND event.class_id = '10' 
     GROUP BY event.event_id,event.event_name,student_class.student_id

这应该给你事件 id 和 name，以及参加它的学生人数。