数据库
– 数据表介绍
– 学生表
– Student(SId,Sname,Sage,Ssex)
– SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
– 课程表
– Course(CId,Cname,TId)
– CId 课程编号,Cname 课程名称,TId 教师编号
– 教师表
– Teacher(TId,Tname)
– TId 教师编号,Tname 教师姓名
– 成绩表
– SC(SId,CId,score)
– SId 学生编号,CId 课程编号,score 分数
CREATE DATABASE fiftyprolem;
– 学生表
– Student(SId,Sname,Sage,Ssex)
– SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
CREATE TABLE Student(SId VARCHAR(10),Sname VARCHAR(10),Sage DATETIME,Ssex VARCHAR(10));
INSERT INTO Student VALUES('01' , '赵雷' , '1990-01-01' , '男');
INSERT INTO Student VALUES('02' , '钱电' , '1990-12-21' , '男');
INSERT INTO Student VALUES('03' , '孙风' , '1990-12-20' , '男');
INSERT INTO Student VALUES('04' , '李云' , '1990-12-06' , '男');
INSERT INTO Student VALUES('05' , '周梅' , '1991-12-01' , '女');
INSERT INTO Student VALUES('06' , '吴兰' , '1992-01-01' , '女');
INSERT INTO Student VALUES('07' , '郑竹' , '1989-01-01' , '女');
INSERT INTO Student VALUES('09' , '张三' , '2017-12-20' , '女');
INSERT INTO Student VALUES('10' , '李四' , '2017-12-25' , '女');
INSERT INTO Student VALUES('11' , '李四' , '2012-06-06' , '女');
INSERT INTO Student VALUES('12' , '赵六' , '2013-06-13' , '女');
INSERT INTO Student VALUES('13' , '孙七' , '2014-06-01' , '女');
– 课程表
– Course(CId,Cname,TId)
– CId 课程编号,Cname 课程名称,TId 教师编号
CREATE TABLE Course(CId VARCHAR(10),Cname NVARCHAR(10),TId VARCHAR(10));
INSERT INTO Course VALUES('01' , '语文' , '02');
INSERT INTO Course VALUES('02' , '数学' , '01');
INSERT INTO Course VALUES('03' , '英语' , '03');
– 教师表
– Teacher(TId,Tname)
– TId 教师编号,Tname 教师姓名
CREATE TABLE Teacher(TId VARCHAR(10),Tname VARCHAR(10));
INSERT INTO Teacher VALUES('01' , '张三');
INSERT INTO Teacher VALUES('02' , '李四');
INSERT INTO Teacher VALUES('03' , '王五');
– 成绩表
– SC(SId,CId,score)
– SId 学生编号,CId 课程编号,score 分数
CREATE TABLE SC(SId VARCHAR(10),CId VARCHAR(10),score DECIMAL(18,1));
INSERT INTO SC VALUES('01' , '01' , 80);
INSERT INTO SC VALUES('01' , '02' , 90);
INSERT INTO SC VALUES('01' , '03' , 99);
INSERT INTO SC VALUES('02' , '01' , 70);
INSERT INTO SC VALUES('02' , '02' , 60);
INSERT INTO SC VALUES('02' , '03' , 80);
INSERT INTO SC VALUES('03' , '01' , 80);
INSERT INTO SC VALUES('03' , '02' , 80);
INSERT INTO SC VALUES('03' , '03' , 80);
INSERT INTO SC VALUES('04' , '01' , 50);
INSERT INTO SC VALUES('04' , '02' , 30);
INSERT INTO SC VALUES('04' , '03' , 20);
INSERT INTO SC VALUES('05' , '01' , 76);
INSERT INTO SC VALUES('05' , '02' , 87);
INSERT INTO SC VALUES('06' , '01' , 31);
INSERT INTO SC VALUES('06' , '03' , 34);
INSERT INTO SC VALUES('07' , '02' , 89);
INSERT INTO SC VALUES('07' , '03' , 98);
问题
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 * FROM student s RIGHT JOIN
( SELECT t1.`SId`, class1, class2 FROM
(SELECT sc.`SId` ,sc.`score` AS class1 FROM sc WHERE sc.`CId`="01" )AS t1, -- 课程01的学生成绩表
(SELECT sc.`SId`,sc.`score` AS class2 FROM sc WHERE sc.`CId` = "02")AS t2 -- 课程02的学生成绩表
WHERE t1.SId = t2.SId AND t1.class1>t2.class2 -- 处理条件同一个学生的成绩 01 大于02的
) r
ON r.SId = s.`SId`;
2 查询同时存在" 01 “课程和” 02 "课程的情况的学生
SELECT * FROM
(SELECT * FROM sc WHERE sc.`CId` = "01") AS t1, -- 01课学生的成绩单
(SELECT * FROM sc WHERE sc.`CId` = "02") AS t2 -- 02课学生的成绩单
WHERE t1.SID = t2.SId; -- 根据学生的ID做个判断
3 查询存在" 01 “课程但可能不存在” 02 "课程的情况(不存在时显示为 null )
SELECT * FROM
(SELECT * FROM sc WHERE sc.`CId` = "01") AS t1
LEFT JOIN
(SELECT * FROM sc WHERE sc.`CId` = "02") AS t2
ON t1.SId = t2.SId;
4查询不存在" 01 “课程但存在” 02 "课程的情况
SELECT * FROM sc
WHERE sc.`SId`
NOT IN( SELECT SId FROM sc WHERE sc.`CId`="01")
AND sc.`CId` = "02";
5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 s.`SId`,s.`Sname`,r.avgs FROM Student s,
(SELECT SId ,AVG(sc.`score`) avgs FROM sc GROUP BY sc.`SId` HAVING avgs>60 ) r
WHERE s.`SId`= r.SId;
6查询在 SC 表存在成绩的学生信息
SELECT DISTINCT student.* FROM student,sc WHERE student.`SId`= sc.`SId`;
7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(没成绩的显示为 null )
SELECT student.SId,student.`Sname`,r.coursenumber,r.asscoresum FROM student ,
(SELECT sc.`SId` ,COUNT(sc.`CId`) AS coursenumber ,SUM(sc.`score`)AS asscoresum FROM sc GROUP BY sc.`SId` ) r
WHERE r.SId = student.`SId`
8查有成绩的学生信息
– 结论：IN()适合B表比A表数据小的情况
– 结论：EXISTS()适合B表比A表数据大的情况
SELECT * FROM student WHERE EXISTS (SELECT sc.`SId`FROM sc WHERE student.`SId` =sc.`SId`);
SELECT * FROM student WHERE student.`SId` IN(SELECT sc.`SId` FROM sc);
9查询「李」姓老师的数量
SELECT COUNT(*) FROM teacher WHERE teacher.`Tname` LIKE "李%";
10查询学过「张三」老师授课的同学的信息
SELECT * FROM student ,Teacher, Course,sc WHERE student.`SId`= sc.`SId` AND sc.`CId`= Course.`CId` AND Course.`TId` = teacher.`TId` AND Tname="张三";
11 查询没有学全所有课程的同学的信息
SELECT * from student,sc where student.SId = sc.sid GROUP BY student.SId having COUNT(sc.CId) <(SELECT COUNT(sc.CId) from sc);
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 student.SId,student.Sname from student ,sc where student.SId=sc.SId and sc.CId in (SELECT sc.CId from sc where sc.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
SELECT
stu.*,
r.t2_count
FROM
student AS stu,(
SELECT DISTINCT
t2.sid AS t2_sid,
count( t2.cid ) AS t2_count
FROM
( SELECT sc.sid, sc.cid FROM sc WHERE sc.sid = 01 ) t1
INNER JOIN ( SELECT sc.sid, sc.cid FROM sc ) t2 ON t1.cid = t2.cid
GROUP BY
t2.sid
) AS r
WHERE
r.t2_count = ( SELECT count( sc.cid ) FROM sc WHERE sc.sid = 05 )
AND stu.sid = r.t2_sid;
14 查询没学过"张三"老师讲授的任一门课程的学生姓名（查询学了张三老师可的学生的的id，剔除出学过该科的学生就是没学过张三老师课的学生）
SELECT
SId,
Sname
FROM
student
WHERE
SId NOT IN (
SELECT DISTINCT
( sc.SId )
FROM
sc,
course,
teacher
WHERE
sc.CId = course.CId
AND teacher.TId = course.TId
AND 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
s.Sid,
s2.Sname,
avg( s.score )
FROM
sc s
JOIN student s2 ON s.Sid = s2.Sid
GROUP BY
s.Sid
HAVING
count( s.score < 60 OR NULL )>= 2;
16检索" 01 "课程分数小于 60，按分数降序排列的学生信息
SELECT
s.*,
score
FROM
student AS s,
sc
WHERE
cid = 01
AND score < 60
AND s.sid = sc.sid
ORDER BY
score DESC
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
-- 法一：先查寻学生们的平均成绩
SELECT
sc.SId,
sc.CId,
sc.score,
sf.ss
FROM
SC,
( SELECT SId, avg( sc.score ) ss FROM sc GROUP BY sc.SId ) sf
WHERE
sc.SId = sf.SId
ORDER BY
sf.ss DESC
-- 法二：
SELECT
sc.SId,
MAX( CASE WHEN sc.CId = '01' THEN sc.score ELSE NULL END ) "语文",
MAX( CASE WHEN sc.CId = '01' THEN sc.score ELSE NULL END ) "数学",
MAX( CASE WHEN sc.CId = '01' THEN sc.score ELSE NULL END ) "英语",
AVG( sc.score ) "平均成绩"
FROM
sc
GROUP BY
sc.SId
ORDER BY
AVG( sc.score ) DESC
18 查询各科成绩最高分、最低分和平均分
SELECT
sc.CId,
max( sc.score ),
MIN( sc.score ),
AVG( sc.score )
FROM
sc
GROUP BY
sc.CId;
– 19 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 c.cid as 课程号, c.cname as 课程名称, count(*) as 选修人数,
max(score) as 最高分, min(score) as 最低分, avg(score) as 平均分,
sum(case when score >= 60 then 1 else 0 end)/count(*) as 及格率,
sum(case when score >= 70 and score < 80 then 1 else 0 end)/count(*) as 中等率,
sum(case when score >= 80 and score < 90 then 1 else 0 end)/count(*) as 优良率,
sum(case when score >= 90 then 1 else 0 end)/count(*) as 优秀率
from sc, course c
where c.cid = sc.cid
group by c.cid
order by count(*) desc, c.cid asc
20. 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
course.CId,
SUM( SId ) num
FROM
sc,
course
GROUP BY
course.CId
ORDER BY
num,
course.CId;
21.按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺
SELECT
a.sid,
a.cid,
a.score,
COUNT(a.score < b.score )+1 AS rank1
FROM
sc a
LEFT JOIN sc b ON a.cid = b.cid
AND a.score < b.score
GROUP BY
a.cid,
a.sid
ORDER BY
a.cid,
a.score DESC;
21 按各科成绩进行排序，并显示排名， Score 重复时合并名次
SELECT
a.sid,
a.cid,
a.score,
count( DISTINCT b.score ) AS rank1
FROM
sc a
LEFT JOIN sc b ON a.cid = b.cid
AND a.score <= b.score
GROUP BY
a.cid,
a.sid
ORDER BY
a.cid,
a.score DESC;
22 查询学生的总成绩，并进行排名，总分重复时保留名次空缺
SELECT
a.*,
count( a.cj < b.cj )+ 1 AS rank1
FROM
( SELECT sid, sum( score ) AS cj FROM sc GROUP BY sid ) a
LEFT JOIN ( SELECT sid, sum( score ) AS cj FROM sc GROUP BY sid ) b ON a.cj < b.cj
GROUP BY
a.sid
ORDER BY
a.cj DESC;
23 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺
SELECT
a.*,
count( DISTINCT b.cj )+ 1 AS rank1
FROM
( SELECT sid, sum( score ) AS cj FROM sc GROUP BY sid ) a
LEFT JOIN ( SELECT sid, sum( score ) AS cj FROM sc GROUP BY sid ) b ON a.cj < b.cj
GROUP BY
a.sid
ORDER BY
a.cj DESC;
24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]，[60-0] 及所占百分比
select sc.cid,cname,count(sid) as '总人数',
concat(round(sum(case when score>=0 and score<60 then 1 else 0 end) /count(sid)*100,2),'%') as '0-60',
concat(round(sum(case when score>=60 and score<70 then 1 else 0 end)/count(sid)*100,2),"%") as '60-70',
concat(round(sum(case when score>=70 and score<85 then 1 else 0 end)/count(sid)*100,2),"%") as '70-85',
concat(round(sum(case when score<=100 and score>=85 then 1 else 0 end )/count(*)*100,2),'%') as '85-100'
from sc join course on sc.cid=course.cid
group by cid;
25 查询各科成绩前三名的记录
select * from
( SELECT
a.*,
count( DISTINCT b.score ) + 1 AS rank1
FROM
sc a
LEFT JOIN sc b ON a.cid = b.cid
AND a.score < b.score
GROUP BY
a.cid,
a.sid
ORDER BY
a.cid,
a.score DESC
) c
WHERE
c.rank1 <= 3;
26 查询每门课程被选修的学生数
select cid, count(*) as '选修人数'
from sc
group by cid;
27查询出只选修两门课程的学生学号和姓名
SELECT
sc.SId,
student.Sname
FROM
student,
sc
WHERE
student.SId = sc.SId
GROUP BY
sc.SId
HAVING
COUNT( SC.CId )= 2;
28 查询男生、女生人数
SELECT
Ssex AS '性别',
COUNT(*) AS '人数'
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 AS '姓名',
COUNT(*) AS '人数'
FROM
student
GROUP BY
Sname;
31查询 1990 年出生的学生名单
SELECT
*
FROM
student
WHERE
YEAR ( sage )= 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
CId,
AVG( sc.score ) AS '平均成绩'
FROM
sc
GROUP BY
CId
ORDER BY
平均成绩,
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.SId,
student.Sname,
AVG( sc.score ) AS '平均成绩'
FROM
student,
sc
WHERE
student.SId = sc.SId
GROUP BY
SC.SId
HAVING
平均成绩 > 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.Sname,
sc.score
FROM
student,
sc,
course
WHERE
student.SId = sc.SId
AND sc.CId = course.CId
AND sc.score < 60
AND course.Cname = '数学'
35 查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）
SELECT
student.Sname,
course.Cname,
sc.score
FROM
student,
sc,
course
WHERE
student.SId = sc.SId
AND sc.CId = course.CId
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.Sname,
course.Cname,
sc.score
FROM
student,
sc,
course
WHERE
student.SId = sc.SId
AND sc.CId = course.CId
AND score>70
37查询不及格的课程
SELECT
course.cname,
sc.score
FROM
sc
JOIN course ON sc.cid = course.cid
WHERE
sc.score < 60;
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.sid,
student.sname
FROM
student,
sc
WHERE
student.sid = sc.sid
AND sc.cid = 01
AND sc.score > 80
ORDER BY
cid;
39求每门课程的学生人数
SELECT
cid,
count(*) AS '选修人数'
FROM
sc
GROUP BY
cid;
40 成绩不重复，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
– 41成绩有重复的情况下，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
SELECT
student.*,
a.score
FROM
sc a
LEFT JOIN sc b ON a.cid = b.cid
AND a.score < b.score #对每门课程下的学生成绩排名
JOIN course ON a.cid = course.cid
JOIN teacher ON course.tid = teacher.tid
AND tname = '张三' #这一行和上一行，是为了筛选张三老师教的课
JOIN student ON a.sid = student.sid # 获取学生信息
GROUP BY
a.cid,
a.sid
HAVING
count( a.score < b.score )= 0 #筛选名次rank=1, count(a.score<b.score)+1=1，两端减去1，简化为count(a.score<b.score)=0
#上面这一行having 子句，这种格式也可以：having count( distinct b.score)=0 ,使用distinct
;
42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
sc.sid,
sc.cid,
sc.score
FROM
sc
JOIN ( SELECT sid, score FROM sc GROUP BY sid, score HAVING count( cid )>= 2 ) a ON sc.sid = a.sid
AND sc.score = a.score
ORDER BY
sid;
43查询每门功成绩最好的前两名
SELECT
a.cid,
a.sid,
sname,
a.score,
count( DISTINCT b.score )+ 1 AS rank1
FROM
( sc a LEFT JOIN sc b ON a.cid = b.cid AND a.score < b.score )
JOIN student ON a.sid = student.sid
GROUP BY
a.cid,
a.sid
HAVING
rank1 <= 2
ORDER BY
cid;
44统计每门课程的学生选修人数（超过 5 人的课程才统计）。
SELECT
sc.cid,
cname,
count( sid ) AS '选修人数'
FROM
sc
JOIN course ON sc.cid = course.cid
GROUP BY
sc.cid
HAVING
count( sid )> 4;
45检索至少选修两门课程的学生学号
SELECT
sid
FROM
sc
GROUP BY
sid
HAVING
count( cid )>= 2;
46查询选修了全部课程的学生信息
SELECT
student.*
FROM
sc
JOIN student ON sc.sid = student.sid
GROUP BY
sid
HAVING
count(*) = ( SELECT count(*) FROM course );
47查询各学生的年龄，只按年份来算
SELECT
student.sid,
student.sname,
student.ssex,
YEAR (
now())- YEAR ( student.sage ) AS 'age'
FROM
student;
48按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
SELECT
student.sid,
student.sname,
student.ssex,
sage,
(
YEAR,
sage,
now()) AS '按月日计算',# 出生月日< 当前日期的月日时，年龄会减一 ,该题目功能是通过这一句实现的，下一句只是为了对比说明两者之间的差别
YEAR (
now())- YEAR ( sage ) AS '按年份计算'
FROM
student;
49查询本周过生日的学生
SELECT
*
FROM
student
WHERE
WEEK (
concat_ws(
'-',
YEAR (
now()),
date_format( sage, '%m-%d' )))= WEEK (
now());
50查询下周过生日的学生
SELECT
*
FROM
student
WHERE
WEEK (
concat_ws(
'-',
YEAR (
now()),
date_format( SAGE, '%m-%d' )))= WEEK (
now())+ 1;
51查询本月过生日的学生
SELECT
*
FROM
student
WHERE
MONTH ( student.sage )= MONTH (
now());
52查询下月过生日的学生
SELECT
*
FROM
student
WHERE
MONTH ( student.sage )= MONTH (
now())+ 1;