/*==========================创建班级表=============================*/
CREATE TABLE class (
cid int(11) NOT NULL AUTO_INCREMENT,
class_name varchar(32) NOT NULL,
PRIMARY KEY (cid)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
INSERT INTO class(cid,class_name) VALUES
(1,"三级二班"),
(2,"三级三班"),
(3,"一级二班"),
(4,"二级九班");
/*创建教师信息表*/
DROP TABLE IF EXISTS teacher;
CREATE TABLE teacher(
tid int(11) NOT NULL AUTO_INCREMENT,
tname varchar(32) NOT NULL,
PRIMARY KEY (tid)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
INSERT INTO teacher VALUES (1, "张磊老师"), (2, "李平老师"), (3, "刘海燕老师"), (4, "朱云海老师"), (5, "李杰老师");
/*========================创建课程信息表=============================*/
CREATE TABLE course (
cid int(11) NOT NULL AUTO_INCREMENT,
cname varchar(32) NOT NULL,
teacher_id int(11) NOT NULL,
PRIMARY KEY (cid),
KEY fk_course_teacher (teacher_id),
CONSTRAINT fk_course_teacher FOREIGN KEY (teacher_id) REFERENCES teacher(tid)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
INSERT INTO course VALUES (1, "生物", 1), (2, "物理", 2), (3, "体育", 3), (4, "美术", 2);
/*=====================创建学生信息表================================*/
DROP TABLE IF EXISTS student;
CREATE TABLE student (
sid int(11) NOT NULL AUTO_INCREMENT,
gender char(1) NOT NULL,
class_id int(11) NOT NULL,
sname varchar(32) NOT NULL,
PRIMARY KEY (sid),
KEY fk_class (class_id),
CONSTRAINT fk_class FOREIGN KEY (class_id) REFERENCES class (cid)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;
INSERT INTO student VALUES (1, "男", 1, "理解"), (2, "女", 1, "钢蛋"),
(3, "男", 1, "张三"), (4, "男", 1, "张一"),
(5, "女", 1, "张二"), (6, "男", 1, "张四"),
(7, "女", 2, "铁锤"), (8, "男", 2, "李三"),
(9, "男", 2, "李一"), (10, "女", 2, "李二"),
(11, "男", 2, "李四"), (12, "女", 3, "如花"),
(13, "男", 3, "刘三"), (14, "男", 3, "刘一"),
(15, "女", 3, "刘二"), (16, "男", 3, "刘四“);
/*=====================创建学生成绩信息表=========================*/
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
`sid` int(11) NOT NULL AUTO_INCREMENT,
`student_id` int(11) NOT NULL,
`course_id` int(11) NOT NULL,
`num` int(11) NOT NULL,
PRIMARY KEY (`sid`),
KEY `fk_score_student` (`student_id`),
KEY `fk_score_course` (`course_id`),
CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;
INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'),
('5', '1', '4', '66'), ('6', '2', '1', '8'),
('8', '2', '3', '68'), ('9', '2', '4', '99'),
('10', '3', '1', '77'), ('11', '3', '2', '66'),
('12', '3', '3', '87'), ('13', '3', '4', '99'),
('14', '4', '1', '79'), ('15', '4', '2', '11'),
('16', '4', '3', '67'), ('17', '4', '4', '100'),
('18', '5', '1', '79'), ('19', '5', '2', '11'),
('20', '5', '3', '67'), ('21', '5', '4', '100'),
('22', '6', '1', '9'), ('23', '6', '2', '100'),
('24', '6', '3', '67'), ('25', '6', '4', '100'),
('26', '7', '1', '9'), ('27', '7', '2', '100'),
('28', '7', '3', '67'), ('29', '7', '4', '88'),
('30', '8', '1', '9'), ('31', '8', '2', '100'),
('32', '8', '3', '67'), ('33', '8', '4', '88'),
('34', '9', '1', '91'), ('35', '9', '2', '88'),
('36', '9', '3', '67'), ('37', '9', '4', '22'),
('38', '10', '1', '90'), ('39', '10', '2', '77'),
('40', '10', '3', '43'), ('41', '10', '4', '87'),
('42', '11', '1', '90'), ('43', '11', '2', '77'),
('44', '11', '3', '43'), ('45', '11', '4', '87'),
('46', '12', '1', '90'), ('47', '12', '2', '77'),
('48', '12', '3', '43'), ('49', '12', '4', '87'),
('52', '13', '3', '87');
/*===================练习题目=====================*/
sql执行顺序:(1)FROM--(2)--ON <join_condition>--(3)<join_type> JOIN <right_table>
--(4)WHERE <where_condition>--(5)GROUP BY <group_by_list>--(6)HAVING <having_condition>
--(7)SELECT --(8)DISTINCT <select_list>--(9)ORDER BY <order_by_condition>--(10)LIMIT <limit_number>
1、查询所有的课程的名称以及对应的任课老师姓名
(way1.)
select
course.cname,teacher.tname
from
course,teacher
where
teacher.tid=course.teacher_id;
(way2.)
SELECT
course.cname,
teacher.tname
FROM
course
INNER JOIN teacher ON course.teacher_id = teacher.tid;
2、查询学生表中男女生各有多少人
(way1.)
select
count(student.gender)
from
student where student.gender="男";
select
count(student.gender)
from
student where student.gender="女";
(way2.)
SELECT
gender as 性别,
count(1) as 人数
FROM
student
GROUP BY
gender;
3、查询物理成绩等于100的学生的姓名
(way1.)
SELECT
student.sname
FROM
student
WHERE
sid IN (
SELECT
student_id
FROM
score
INNER JOIN course ON score.course_id = course.cid
WHERE
course.cname = '物理'
AND score.num = 100
);
(way2.)
select
student.sname
from
student
where
sid in (select
student_id
from
score
where score.num=100 and score.course_id=2);
4、查询平均成绩大于八十分的同学的姓名和平均成绩
select student.sname,score_avg.avg_num
from
student,
(
select
student_id,avg(score.num) AS avg_num
from
score
group by
score.student_id
having avg(score.num)>80
) AS score_avg
WHERE student.sid=score_avg.student_id;
(way2.)
SELECT
student.sname,
t1.avg_num
FROM
student
INNER JOIN (
SELECT
student_id,
avg(num) AS avg_num
FROM
score
GROUP BY
student_id
HAVING
avg(num) > 80
) AS t1 ON student.sid = t1.student_id;
5、查询所有学生的学号，姓名，选课数，总成绩
(way1.)
SELECT
student.sid,
student.sname,
t2.course_num,
t2.total_num
FROM
student
LEFT JOIN (
SELECT
student_id,
COUNT(course_id) course_num,
sum(num) total_num
FROM
score
GROUP BY
student_id
)AS t2
ON student.sid = t2.student_id;
6、 查询姓李老师的个数
SELECT COUNT(tid)
FROM teacher
WHERE tname LIKE "李%";
7、 查询没有报李平老师课的学生姓名
(way1.)
SELECT sname
FROM student
WHERE student.sid
NOT IN (SELECT DISTINCT student_id /*DISTINCT筛选不重复的记录*/
FROM score
WHERE course_id=2 OR course_id=4
);
(way2.)
SELECT
student.sname
FROM
student
WHERE
sid NOT IN (
SELECT DISTINCT
student_id
FROM
score
WHERE
course_id IN (
SELECT
course.cid
FROM
course
INNER JOIN teacher ON course.teacher_id = teacher.tid
WHERE
teacher.tname = '李平老师'
)
);
8、 查询物理课程比生物课程高的学生的学号
(way1.)
SELECT
table1.student_id
FROM
(
SELECT
student_id,num
AS
subject_num
FROM
score
WHERE
course_id=2
) AS table1
INNER JOIN
(
SELECT
student_id,num
AS
biology_num
FROM
score
WHERE
course_id=1
) AS table2
ON
table1.student_id=table2.student_id
WHERE
table1.subject_num>table2.biology_num;
(way2.)
SELECT
t1.student_id
FROM
(
SELECT
student_id,
num
FROM
score
WHERE
course_id = (
SELECT
cid
FROM
course
WHERE
cname = '物理'
)
) AS t1
INNER JOIN (
SELECT
student_id,
num
FROM
score
WHERE
course_id = (
SELECT
cid
FROM
course
WHERE
cname = '生物'
)
) AS t2 ON t1.student_id = t2.student_id
WHERE
t1.num > t2.num;
9、 查询没有同时选修物理课程和体育课程的学生姓名
(way1.)
SELECT
sname
FROM
student
WHERE
sid NOT IN
(
SELECT
t1.student_id
FROM
(
SELECT
student_id,course_id
FROM
score
WHERE
course_id
IN (
SELECT
cid
FROM
course
WHERE
cname="物理"
)
) AS t1
INNER JOIN
(
SELECT
student_id,course_id
FROM
score
WHERE
course_id
IN (
SELECT
cid
FROM
course
WHERE
cname="体育"
)
) AS t2
ON t1.student_id=t2.student_id
);
(way2.)
思路(没有同时选修指的是选修了一门的，思路是得到物理+体育课程的学生信息表，然后基于学生分组，统计count(课程)=1)
SELECT
student.sname
FROM
student
WHERE
sid IN (
SELECT
student_id
FROM
score
WHERE
course_id IN (
SELECT
cid
FROM
course
WHERE
cname = '物理'
OR cname = '体育'
)
GROUP BY
student_id
HAVING
COUNT(course_id) = 1
);
10、查询挂科超过两门(包括两门)的学生姓名和班级
(way1.)
SELECT
class_name,t1.sname
FROM
class
INNER JOIN (
SELECT
sname,class_id
FROM
student
WHERE
sid IN
(
SELECT
student_id
FROM
score
WHERE
score.num<60
GROUP BY
student_id
HAVING COUNT(num)=2
)
)AS t1 ON class.cid=t1.class_id;
(way2.)思路求出<60的表，然后对学生进行分组，统计课程数目>=2
SELECT
student.sname,
class.class_name
FROM
student
INNER JOIN (
SELECT
student_id
FROM
score
WHERE
num < 60
GROUP BY
student_id
HAVING
count(course_id) >= 2
) AS t1
INNER JOIN class ON student.sid = t1.student_id
AND student.class_id = class.cid;
11、查询选修了所有课程的学生姓名
(way1.)
select
student.sname
from
student
where
sid in
(
select
student_id
from
score
group by
student_id
having
count(course_id)=4
);
(way2.)
SELECT
student.sname
FROM
student
WHERE
sid IN (
SELECT
student_id
FROM
score
GROUP BY
student_id
HAVING
COUNT(course_id) = (SELECT count(cid) FROM course)
);
12、查询李平老师教的课程的所有成绩记录
(way1.)
select
course_id,num
from
score
where
score.course_id in
(
select
cid
from
course
inner join
teacher
on
course.teacher_id=teacher.tid
where
teacher.tname="李平老师"
);
(way2.)
SELECT
*
FROM
score
WHERE
course_id IN (
SELECT
cid
FROM
course
INNER JOIN teacher ON course.teacher_id = teacher.tid
WHERE
teacher.tname = '李平老师'
);
13、查询全部学生都选修了的课程号和课程名
（way1.)
select
cid,cname
from
course
where
cid in
(
select
course_id
from
score
group by
course_id
having count(student_id)= (select count(sid) from student)
);
(way2.)
SELECT
cid,
cname
FROM
course
WHERE
cid IN (
SELECT
course_id
FROM
score
GROUP BY
course_id
HAVING
COUNT(student_id) = (
SELECT
COUNT(sid)
FROM
student
)
);
14、查询每门课程被选修的次数
(way1.)
select
course_id,count(student_id)
from
score
group by
course_id;
15、查询只选修了一门课程的学生姓名和学号
select
sid,sname
from
student
where
sid in
(
select
student_id
from
score
group by
student_id
having
count(course_id)=1
);
16、查询所有学生考出的总成绩并按从高到低排序（成绩去重）
(way1.)
select
sid,sname,t1.num
from
student
left join
(
select
student_id,sum(score.num) as num
from
score
group by
student_id
) as t1 on student.sid=t1.student_id
order by t1.num desc;
17、查询平均成绩大于85的学生姓名和平均成绩
select
sname,t1.num
from
student
inner join
(
select
student_id,avg(num) as num
from
score
group by
student_id
having
avg(num)>85
) as t1 on student.sid=t1.student_id;
18、查询生物成绩不及格的学生姓名和对应生物分数
(way1.)
select
sname,t1.num
from
student
inner join
(
select
student_id,num
from
score
where
course_id=(select cid from course where cname="生物") and num<60
)as t1 on student.sid=t1.student_id;
(way2.)
SELECT
sname 姓名,
num 生物成绩
FROM
score
LEFT JOIN course ON score.course_id = course.cid
LEFT JOIN student ON score.student_id = student.sid
WHERE
course.cname = '生物'
AND score.num < 60;
19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
(way1.)
select
sname
from
student
where
sid in
(
select
t1.student_id
from
(
select
student_id,num
from
score
where
course_id in
(
select
cid
from
course
where
course.teacher_id=(select tid from teacher where tname="李平老师")
)
group by student_id
order by
AVG(num) DESC
limit 1
)as t1
);
(way2.)
SELECT
sname
FROM
student
WHERE
sid = (
SELECT
student_id
FROM
score
WHERE
course_id IN (
SELECT
course.cid
FROM
course
INNER JOIN teacher ON course.teacher_id = teacher.tid
WHERE
teacher.tname = '李平老师'
)
GROUP BY
student_id
ORDER BY
AVG(num) DESC
LIMIT 1
);
20、查询每门课程成绩最好的前两名学生姓名
SELECT
*
FROM
score
ORDER BY
course_id,
num DESC;
#表1：求出每门课程的课程course_id,与最高分数first_num
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id;
#表2：去掉最高分，再按照课程分组，取得的最高分，就是第二高的分数second_num
SELECT
score.course_id,
max(num) second_num
FROM
score
INNER JOIN (
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t ON score.course_id = t.course_id
WHERE
score.num < t.first_num
GROUP BY
course_id;
#将表1和表2联合到一起，得到一张表t3，包含课程course_id与该们课程的first_num与second_num
SELECT
t1.course_id,
t1.first_num,
t2.second_num
FROM
(
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t1
INNER JOIN (
SELECT
score.course_id,
max(num) second_num
FROM
score
INNER JOIN (
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t ON score.course_id = t.course_id
WHERE
score.num < t.first_num
GROUP BY
course_id
) AS t2 ON t1.course_id = t2.course_id;
#查询前两名的学生（有可能出现并列第一或者并列第二的情况）
SELECT
score.student_id,
t3.course_id,
t3.first_num,
t3.second_num
FROM
score
INNER JOIN (
SELECT
t1.course_id,
t1.first_num,
t2.second_num
FROM
(
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t1
INNER JOIN (
SELECT
score.course_id,
max(num) second_num
FROM
score
INNER JOIN (
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t ON score.course_id = t.course_id
WHERE
score.num < t.first_num
GROUP BY
course_id
) AS t2 ON t1.course_id = t2.course_id
) AS t3 ON score.course_id = t3.course_id
WHERE
score.num >= t3.second_num
AND score.num <= t3.first_num;
#排序后可以看的明显点
SELECT
score.student_id,
t3.course_id,
t3.first_num,
t3.second_num
FROM
score
INNER JOIN (
SELECT
t1.course_id,
t1.first_num,
t2.second_num
FROM
(
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t1
INNER JOIN (
SELECT
score.course_id,
max(num) second_num
FROM
score
INNER JOIN (
SELECT
course_id,
max(num) first_num
FROM
score
GROUP BY
course_id
) AS t ON score.course_id = t.course_id
WHERE
score.num < t.first_num
GROUP BY
course_id
) AS t2 ON t1.course_id = t2.course_id
) AS t3 ON score.course_id = t3.course_id
WHERE
score.num >= t3.second_num
AND score.num <= t3.first_num
ORDER BY
course_id;
#可以用以下命令验证上述查询的正确性
SELECT
*
FROM
score
ORDER BY
course_id,
num DESC;