SQL 练习

原文链接
网上找来SQL50道练习题，逐个练习，做一记录。

1.学生表
student(sid,sname,sage,ssex)
学生编号,学生姓名, 出生年月,学生性别
2.课程表
course(cid,cname,tid)
课程编号, 课程名称, 教师编号
3.教师表
teacher(tid,tname)
教师编号,教师姓名
4.成绩表
sc(sid,cid,score)
学生编号,课程编号,分数

1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数

SELECT a.aid,a.ascore,b.bscore FROM
(SELECT sc.sid aid,sc.score ascore FROM sc WHERE CId = 01)a
INNER JOIN 
(SELECT sc.SId bid,sc.score bscore FROM sc WHERE CId = 02)b
ON a.aid = b.bid
WHERE a.ascore > b.bscore

或者 null值按0算
SELECT a.aid,a.ascore,c.cscore FROM
(SELECT sc.sid aid,sc.score ascore FROM sc WHERE CId = 01)a
LEFT   JOIN 
(

SELECT student.sid cid, IFNULL(b.bscore,0) cscore FROM student
LEFT JOIN (SELECT sc.sid bid ,sc.cid,sc.score bscore FROM sc WHERE CId = 02)b
ON b.bid = student.SId

)c
ON a.aid = c.cid
WHERE a.ascore > c.cscore

2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数

SELECT a.aid,a.ascore,b.bscore FROM
(SELECT sc.sid aid,sc.score ascore FROM sc WHERE CId = 01)a
INNER JOIN 
(SELECT sc.SId bid,sc.score bscore FROM sc WHERE CId = 02)b
ON a.aid = b.bid
WHERE a.ascore < b.bscore

3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩

SELECT student.*,AVG(sc.score) avg FROM student
JOIN sc ON sc.SId = student.SId
GROUP BY sc.SId
HAVING avg < 60

4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩(包括有成绩的和无成绩的)

=========Having 后附加条件=========

SELECT student.*,AVG(sc.score) FROM student
LEFT   JOIN sc ON sc.SId = student.SId
GROUP BY student.SId
HAVING AVG(sc.score) < 60 OR  ISNULL(AVG(sc.score))

5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩

SELECT student.*,COUNT(sc.CId),SUM(sc.score) FROM student
LEFT   JOIN sc ON sc.SId = student.SId
GROUP BY student.SId

6、查询"李"姓老师的数量

SELECT COUNT(*) FROM teacher WHERE Tname LIKE '李%'

7、查询学过"张三"老师授课的同学的信息

SELECT student.* FROM sc
RIGHT JOIN student ON sc.SId = student.SId
RIGHT JOIN course ON course.CId = sc.CId
RIGHT JOIN teacher ON teacher.TId = course.TId
WHERE teacher.Tname = '张三'

8、查询没学过"张三"老师授课的同学的信息

SELECT student.* FROM student 
WHERE SId NOT IN 
(
SELECT student.SId FROM sc
RIGHT JOIN student ON sc.SId = student.SId
RIGHT JOIN course ON course.CId = sc.CId
RIGHT JOIN teacher ON teacher.TId = course.TId
WHERE teacher.Tname = '张三'
)

9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息

SELECT student.* FROM sc 
LEFT JOIN student ON student.SId = sc.SId
WHERE CId = 01
AND sc.SId  IN (SELECT sc.SId  FROM sc WHERE CId = 02)

10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息

SELECT student.* FROM sc 
LEFT JOIN student ON student.SId = sc.SId
WHERE CId = 01
AND sc.SId NOT IN (SELECT sc.SId  FROM sc WHERE CId = 02)

11、查询没有学全所有课程的同学的信息

SELECT student.*,COUNT(sc.CId) co FROM student
RIGHT JOIN sc ON sc.SId = student.SId
GROUP BY SId
HAVING co < (SELECT COUNT(*) FROM course)

12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息

SELECT DISTINCT a.sid,student.Sname FROM sc a
LEFT JOIN student
ON student.SId = a.SId
WHERE a.CId IN (SELECT DISTINCT sc.cid  FROM sc  WHERE sc.SId = 01)
AND a.SId != 01
13、查询和"01"号的同学学习的课程完全相同的其他同学的信息

14、查询没学过"张三"老师讲授的任一门课程的学生姓名

SELECT student.* FROM student WHERE SId NOT IN
(
SELECT student.SId  FROM teacher
RIGHT JOIN course ON course.TId = teacher.TId
RIGHT JOIN sc ON sc.CId = course.CId
RIGHT JOIN student ON student.SId = sc.SId
WHERE teacher.Tname = '张三'
)

15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

SELECT sc.SId,student.Sname,
       SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END ) AS co
FROM   sc
LEFT JOIN student ON student.SId = sc.SId
GROUP BY sc.SId
HAVING co > 1

16、检索"01"课程分数小于60，按分数降序排列的学生信息

SELECT student.* ,sc.cid,course.Cname,sc.score FROM student
RIGHT JOIN sc ON sc.SId = student.SId
RIGHT JOIN course ON sc.CId = course.CId
WHERE sc.CId =01
AND score < 60

17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

SELECT sc.SId, round(AVG(sc.score),2) avg,
    SUM(CASE WHEN CId = 01 THEN score ELSE 0 END) AS '01',
    SUM(CASE WHEN CId = 02 THEN score ELSE 0 END) AS '02',
    SUM(CASE WHEN CId = 03 THEN score ELSE 0 END) AS '03'
FROM sc
GROUP BY sid
ORDER BY avg

18.查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率
--及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90

SELECT sc.CId,course.Cname, 
    MAX(sc.score) '最高分',
    MIN(sc.score) '最低分',
    AVG(sc.score) '平均分',
    ROUND(SUM(CASE WHEN score >= 90 THEN 1 ELSE 0 END )/COUNT(*) * 100,2)   '优率',
    ROUND(SUM(CASE WHEN score >= 80 AND score < 90 THEN 1 ELSE 0 END)/COUNT(*)* 100,2) '良率',
    ROUND(SUM(CASE WHEN score >= 70 AND score < 80 THEN 1 ELSE 0 END)/COUNT(*)*100,2) '中率',
    ROUND(SUM(CASE WHEN score >= 60 AND score < 70 THEN 1 ELSE 0 END)/COUNT(*)*100,2) '及格率'

FROM sc
LEFT JOIN course
ON course.CId = sc.CId
GROUP BY sc.CId

20、查询学生的总成绩并进行排名

SELECT a.sid,
             @i := @i+1 as i,
             @k := (CASE WHEN  @score = a.sum THEN @k ELSE @i END)  as rank,
             @score := a.sum as score
FROM
(
SELECT sc.sid,SUM(sc.score) sum, ROUND(AVG(sc.score),2) avg FROM sc
GROUP BY sc.SId
ORDER BY avg DESC
)a,
(SELECT @k:=0, @i:=0,@score :=0)b

21、查询不同老师所教不同课程平均分从高到低显示

SELECT teacher.Tname,course.Cname,AVG(sc.score)
FROM teacher
LEFT JOIN course ON teacher.TId = course.TId
LEFT JOIN sc ON sc.CId = course.CId
GROUP BY sc.CId
ORDER BY AVG(sc.score)
22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩

23、统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比

SELECT sc.CId,course.Cname,
    SUM(CASE WHEN score >= 85 THEN 1 ELSE 0 END )AS '85-100',
    ROUND(SUM(CASE WHEN score >= 85 THEN 1 ELSE 0 END )/COUNT(*) * 100,2)   'per1',
    
    SUM(CASE WHEN score >= 70 AND score < 85 THEN 1 ELSE 0 END) AS '70-85',
    ROUND(SUM(CASE WHEN score >= 70 AND score < 85 THEN 1 ELSE 0 END)/COUNT(*)* 100,2) 'per2',

    SUM(CASE WHEN score >= 60 AND score < 70 THEN 1 ELSE 0 END) AS '60-70',
    ROUND(SUM(CASE WHEN score >= 60 AND score < 70 THEN 1 ELSE 0 END)/COUNT(*)*100,2) 'per3',
 
    SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END) AS '0-60',
    ROUND(SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END)/COUNT(*)*100,2)  'per4'
FROM sc
LEFT JOIN course
ON course.CId = sc.CId
GROUP BY sc.cid
24、查询学生平均成绩及其名次(变量的使用)
SELECT  a.sid,
        @i:=@i+1 AS '不保留空缺排名',
        @k:=(case when @avg_score=a.avg_s then @k else @i end)  AS  '保留空缺排名',
        @avg_score:=avg_s  AS  '平均分'
FROM 
(
select sid, ROUND(AVG(score),2) AS avg_s 
from sc
GROUP BY sid 
ORDER BY avg_s DESC
)a,
(select @avg_score:=0,@i:=0,@k:=0)b;
25、查询各科成绩前三名的记录(同42)
SELECT a.sid,a.cid,a.score,b.sid,b.cid,b.score FROM sc a
LEFT JOIN sc b
ON a.CId = b.CId AND a.score < b.score
GROUP BY a.SId,a.CId,a.score
HAVING COUNT(b.SId) < 3
ORDER BY a.CId,a.score DESC

26、查询每门课程被选修的学生数

SELECT sc.cid,course.Cname,COUNT(sc.sid) FROM sc
LEFT JOIN course
ON sc.CId = course.CId
GROUP BY sc.cId

27、查询出只有两门课程的全部学生的学号和姓名

SELECT sc.SId ,COUNT(sc.CId) co FROM sc
LEFT JOIN student
ON student.SId = sc.SId
GROUP BY SId
HAVING co = 2

28、查询男生、女生人数

SELECT Ssex，COUNT(Ssex) FROM student GROUP BY Ssex

29、查询名字中含有"风"字的学生信息

SELECT * FROM student WHERE Sname LIKE '%风%'

30、查询同名同性学生名单，并统计同名人数

SELECT Sname,COUNT(*) FROM student GROUP BY Sname HAVING COUNT(*) > 1

31、查询1990年出生的学生名单

SELECT student.* FROM student WHERE YEAR(Sage) = 1990
或者
SELECT student.* FROM student WHERE Sage LIKE '1990%'

32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

SELECT course.CId,course.Cname,AVG(sc.score) 
FROM sc
LEFT JOIN course
ON course.CId = sc.CId
GROUP BY CId
ORDER BY AVG(sc.score) DESC, course.CId

33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩

SELECT student.* FROM student 
WHERE SId IN
(
SELECT sid FROM sc
GROUP BY SId
HAVING AVG(score) > 85
)

34、查询课程名称为"数学"，且分数低于60的学生姓名和分数

SELECT student.sid,student.Sname,sc.score,course.CId,course.Cname
FROM student
LEFT JOIN sc ON sc.SId = student.SId
LEFT JOIN course ON sc.CId = course.CId
WHERE course.Cname = '数学'
AND score < 60
35、查询所有学生的课程及分数情况；
SELECT student.sid,student.Sname,
sum(case WHEN course.Cname = '语文' THEN sc.score ELSE 0 END ) AS '语文', 
sum(case WHEN course.Cname = '数学' THEN sc.score ELSE 0 END ) AS '数学',
sum(case WHEN course.Cname = '英语' THEN sc.score ELSE 0 END ) AS '英语',
sum( sc.score ) AS '总分'
FROM student
LEFT JOIN sc     on sc.sid = student.SId
LEFT JOIN course on course.cid = sc.CId
GROUP BY SId

36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数

SELECT student.* FROM student
RIGHT JOIN 
(
SELECT sid ,MAX(score) FROM sc
GROUP BY SId
HAVING MAX(score) > 70
) t1
ON t1.sid = student.SId

37、查询不及格的课程

SELECT course.cid,course.Cname FROM course
RIGHT JOIN 
(
SELECT cid tid FROM sc
WHERE score  < 60
GROUP BY CId
)t1
ON t1.tid = course.CId

38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名；

SELECT student.* ,sc.score FROM student,course,sc
WHERE student.sid = sc.SId
AND sc.CId = course.CId
AND  course.CId = 01
AND  sc.score > 70

或者：
SELECT student.* ,sc.score FROM sc
LEFT JOIN student
ON sc.SId = student.SId
WHERE sc.cId = 01
AND  sc.score > 70

39、求每门课程的学生人数

SELECT cid,COUNT(sid) FROM sc
GROUP BY CId

40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩,假定只有一个最高分

select student.*, sc.score, sc.cid from student, teacher, course,sc 
where teacher.tid = course.tid
and sc.sid = student.sid
and sc.cid = course.cid
and teacher.tname = "张三"
order by score desc
limit 1;

41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

SELECT DISTINCT a.sid,a.cid,a.score FROM sc a
LEFT JOIN sc b
ON a.CId != b.CId AND a.score = b.score
42、查询每门功成绩最好的前两名
select a.sid,a.cid,a.score from sc a
where (select COUNT(*) from sc b where b.cid=a.cid and b.score>=a.score)<=2 
ORDER BY a.cid

43、统计每门课程的学生选修人数（超过5人的课程才统计）。
要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

SELECT cid,COUNT(sid) per FROM sc
GROUP BY CId
HAVING COUNT(sid) >= 5
ORDER BY per desc,cid;

44、检索至少选修两门课程的学生学号

SELECT sid,COUNT(CId) FROM sc
GROUP BY SId
HAVING COUNT(CId) >=2

45、查询选修了全部课程的学生信息

SELECT * FROM student WHERE
SId IN
(
SELECT sid FROM sc
GROUP BY SId
HAVING COUNT(CId) = (SELECT COUNT(*) FROM course)
)

46、查询各学生的年龄

SELECT student.sid, student.Sname,TIMESTAMPDIFF(YEAR,Sage,NOW())
from student

47、查询本周过生日的学生

SELECT * from student WHERE WEEKOFYEAR(Sage) = WEEKOFYEAR(NOW())

48、查询下周过生日的学生

SELECT * from student WHERE WEEKOFYEAR(Sage) = WEEKOFYEAR(NOW())+1

49、查询本月过生日的学生

SELECT * FROM student WHERE MONTH(Sage) = MONTH(now())

50、查询下月过生日的学生

SELECT * FROM student WHERE MONTH(sage) = MONTH(NOW())+1
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