请教一个 SQL 问题 - V2EX
sockball07

请教一个 SQL 问题

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  •   sockball07 Sep 19, 2020 1963 views
    This topic created in 2063 days ago, the information mentioned may be changed or developed.

    现有 2 张表

    course course_id int 课程 ID score float 课程得分,满分 100,60 及格 student_id int 学生 ID student student_id int 学生 ID name int 学生姓名 

    一个学生可能有多个课程得分(即 student 一对多于 course )

    现定义一个学生及格的条件为所有课程中只要有一门课程及格则算及格,只有所有课程不及格的情况下才算不及格

    求所有及格的学生和所有不及格的学生。

    及格很简单

    SELECT s.student_id, s.name FROM student s INNER JOIN course c ON s.student_id = c.student_id WHERE c.score >= 60 GROUP BY student_id 

    但是不及格却不能直接以 WHERE c.score < 60 GROUP BY student_id 得出结果

    问除了使用 ( NOT IN 及格的学生)的结果 还有什么比较好的方法?

    此处只是模拟真实场景,实际上的条件比score >= 60要多,所以不应该特别针对此处使用MIN来做...(如果回复有我会再说明的)

    Supplement 1    Oct 6, 2020
    抱歉,回复不及时

    其他回答比较针对这道题了,实际条件(及格)要比 score >= 6 0 要多(多个条件),已使用 exists
    5 replies    2020-09-20 11:12:21 +08:00
    wisunny
        1
    wisunny  
       Sep 19, 2020 via Android
    exists
    TimePPT
        2
    TimePPT  
    PRO
       Sep 19, 2020 via Android/span>   2
    想了下,试试用 case when then else 把及格不及格二值化(及格赋值 1,不及格 0 ),然后 group by 求和,和大于 0 的及格,等于 0 的不及格
    chotow
        3
    chotow  
       Sep 19, 2020
    SELECT s.name, c.score, c.course_id
    FROM course AS c
    JOIN student AS s ON s.student_id = c.student_id
    LEFT JOIN course AS c_tmp ON c_tmp.student_id = c.student_id AND c.score < c_tmp.score
    WHERE c_tmp.course_id IS NULL
    AND c.score < 60

    https://dev.mysql.com/doc/refman/8.0/en/example-maximum-column-group-row.html
    wspsxing
        4
    wspsxing  
       Sep 20, 2020
    select student_id, name, pass, cc from (select student_id, sum(score >= 60) as pass, count(score) as cc from course group by student_id)a join student as s on a.student_id = s.id where pass <= 0
    awen233333
        5
    awen233333  
       Sep 20, 2020 via Android
    having max(c.score)<60
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