mysql练习，查询某班级中各科成绩最高的学生信息

班级表class

成绩表source

 

学生表student

---

 1、查询班级一班的各科成绩最高的学生信息

使用左连接 left join
SELECT 
    a.stuid,
    a.stuname,
    a.course,
    a.source,
  a.classname
FROM (
SELECT
    student.stuid,
    student.stuname,
    source.course,
    source.source,
  class.classname
FROM
    student
LEFT JOIN class ON class.classid = student.classid
LEFT JOIN source ON
student.stuid = source.stuid
WHERE class.classname = '一班' ) AS a
LEFT JOIN (
SELECT
    student.stuid,
    student.stuname,
    source.course,
    source.source,
  class.classname
FROM
    student
LEFT JOIN class ON class.classid = student.classid
LEFT JOIN source ON
student.stuid = source.stuid
WHERE class.classname = '一班' ) AS b 
ON a.source < b.source 
AND a.course = b.course 
WHERE
    b.course IS NULL

SELECT a.stuid, a.stuname, a.classname, a.course, a.source FROM(
SELECT student.stuid, student.stuname, class.classname, source.course, source.source FROM student
JOIN class ON class.classid = student.classid AND class.classname = '一班'
JOIN source ON source.stuid = student.stuid) AS a
JOIN (
    SELECT b.stuid, b.stuname, b.classname, b.course, max(b.source) as max_source FROM(
    SELECT student.stuid, student.stuname, class.classname, source.course, source.source FROM student
    JOIN class ON class.classid = student.classid AND class.classname = '一班'
    JOIN source ON source.stuid = student.stuid) AS b
    GROUP BY b.course
) AS c
ON c.course = a.course AND c.max_source = a.source