1. 表结构和数据 -> 将文件导入数据库即可
/*
Navicat Premium Data Transfer
Source Server : localhost
Source Server Type : MySQL
Source Server Version : 50624
Source Host : localhost
Source Database : sqlexam
Target Server Type : MySQL
Target Server Version : 50624
File Encoding : utf-8
Date: 10/21/2016 06:46:46 AM
*/
SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for `class`
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
`cid` int(11) NOT NULL AUTO_INCREMENT,
`caption` varchar(32) NOT NULL,
PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of `class`
-- ----------------------------
BEGIN;
INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
COMMIT;
-- ----------------------------
-- Table structure for `course`
-- ----------------------------
DROP TABLE IF EXISTS `course`;
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;
-- ----------------------------
-- Records of `course`
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
COMMIT;
-- ----------------------------
-- Table structure for `score`
-- ----------------------------
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;
-- ----------------------------
-- Records of `score`
-- ----------------------------
BEGIN;
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');
COMMIT;
-- ----------------------------
-- Table structure for `student`
-- ----------------------------
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;
-- ----------------------------
-- Records of `student`
-- ----------------------------
BEGIN;
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');
COMMIT;
-- ----------------------------
-- Table structure for `teacher`
-- ----------------------------
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;
-- ----------------------------
-- Records of `teacher`
-- ----------------------------
BEGIN;
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');
COMMIT;
SET FOREIGN_KEY_CHECKS = 1;
2. 练习题
- 查询成绩表大于60分的数据
select * from score where num > 60;
- 查询老师对应的科目名称 -> 使用 inner join 可以不显示有null数据的这一行
select
teacher.tname,
course.cname
from
teacher
left join course on teacher.tid = course.cid;
- 查看所有学生所对应的班级
select
student.sid,
student.sname,
class.caption
from
student
left join class on student.class_id = class.cid;
- 查询老师的任课个数，并且把对应的科目名称显示出来
select
b.teacher_id,
teacher.tname,
b.quantity
from
( select teacher_id, count( cid ) as quantity from course group by teacher_id ) as b
left join teacher on b.teacher_id = teacher.tid;
- 查询男生的个数和女生的个数
select gender, count(gender) as quantity from student group by gender;
- 查询平均成绩大于60分的学生的学号和平均成绩
select
student.sid,
student.sname,
b.average
from
( select student_id, avg( num ) as average from score group by student_id having avg( num ) > 60 ) as b
left join student on b.student_id = student.sid;
- 查询所有学生的学号、姓名、选课数、总成绩
select
student.sid,
student.sname,
count( student.sid ) as e_coures_num,
sum( score.num ) as overall_result
from
score
left join student on score.student_id = student.sid
group by
student.sid;
- 查询姓“李”的老师的个数
select count(tid) from teacher where tname like '李%';
- 查询没学过“叶平”老师课的学生的学号、姓名 -> （查询叶平老师的所有课程id -> 查询所有选了叶平老师课的学生id -> 使用 not in 查询不在这堆选了叶平老师课的学生id的数据）
select
student.sid,
student.sname
from
student
where
sid not in (
select
student_id
from
score
where
course_id in (
select
course.cid
from
course
left join teacher on course.teacher_id = teacher.tid
where
teacher.tname = '李平老师'
)
group by
student_id
);
- 查询生物课程比物理课程成绩高的所有学生的学号 -> （关联成绩表和课程表得到课程名称等于生物的数据然后将该数据作为临时表A -> 关联成绩表和课程表得到课程名称等于物理的数据然后将该数据作为临时表B -> 将临时表A和临时表B关联起来然后查询生物成绩高于物理成绩的学生id）
select A.student_id from
(select score.sid,score.student_id,course.cname,score.num from score left join course on score.course_id = course.cid where course.cname = '生物') as A
inner join
(select score.sid,score.student_id,course.cname,score.num from score left join course on score.course_id = course.cid where course.cname = '物理') as B
on A.student_id = B.student_id
where A.num > B.num;
# 美化后的代码
select
a.student_id
from
(
select
score.sid,
score.student_id,
course.cname,
score.num
from
score
left join course on score.course_id = course.cid
where
course.cname = '生物'
) as a
inner join (
select
score.sid,
score.student_id,
course.cname,
score.num
from
score
left join course on score.course_id = course.cid
where
course.cname = '物理'
) as b on a.student_id = b.student_id
where
a.num > b.num;
- 查询学过课程编号为1并且也学过课程编号为2的学生的学号、姓名 -> (先查询既选择课程编号为1又选择课程编号为2的所有学生 -> 根据学生进行分组，如果学生数量等于2表示，两门均已选择)
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (1, 2)
group by
student_id
having
count(1) > 1
);
- 查询学过叶平老师所教的所有课的学生的学号、姓名 -> (查询叶平老师的id -> 使用叶平老师的id查询它所教的课程id -> 使用叶平老师所教的课程id查询叶平老师所教的所有课的学生的学号、姓名)
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (
select
cid
from
course
where
teacher_id in (
select
tid
from
teacher
where
tname = '李平老师'
)
)
group by
student_id
)
- 查询课程编号为2的成绩比课程编号为1的成绩低的所有学生的学号、姓名 -> (查询成绩表课程编号为2的数据作为临时表A -> 查询成绩表课程编号为1的数据作为临时表B -> 将临时表B和临时表A关联起来然后查询课程编号2的成绩高于课程编号1的成绩的学生id -> 将查询到课程编号2的成绩高于课程编号1的成绩的学生id作为临时表与学生表关联起来得到课程编号2的成绩高于课程编号1的成绩的学生id和姓名)
select
S.student_id,
student.sname
from
(
select
A.student_id
from
(
select
*
from
score
where
course_id = 2
) as A
left join (
select
*
from
score
where
course_id = 1
) as B on A.student_id = B.student_id
where
A.num > B.num
) as S
left join student on S.student_id = student.sid
- 查询有课程成绩小于60分的学生的学号、姓名
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
num < 60
group by
student_id
);
- 查询没有学全所有课的学生的学号、姓名 -> (查询课程的总数 -> 以student_id为前提对成绩表进行分组，查询学生所选的课程数小于总课程数的数据)
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
GROUP BY
student_id
having
count(student_id) < (
select
count(1)
from
course
)
)
- 查询至少有一门课与学号为1的学生所学相同的学生的学号和姓名 -> (将成绩表和表关联起来 -> 查询学号为1的学生所有的课程id，通过该id查询除了学号为1的学生所有学了这些课程的学生) -> 可以先进行连表在进行数据筛选
select
student.sid,
student.sname
from
score
left join student on score.student_id = student.sid
where
student_id != 1
and course_id in (
select
course_id
from
score
where
student_id = 1
)
group by
student_id;
- 查询学习了与学号为2的学生完全相同课程的学生的序号和姓名 -> (查询学号为2的学生所学课程的id -> 通过学号为2的学生所学课程的id判断查询出学过这些课程学生id,然后对这些学生进行分组，查询出课程数等于学号为2的学生所学课程数的学生id)
# 写法一
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
student_id != 2
and course_id in (
select
course_id
from
score
where
student_id = 2
)
group by
student_id
having
count(1) = (
select
count(1)
from
score
where
student_id = 2
)
);
# 写法二 -> 先将成绩表和学生表进行关联在进行数据的筛选
select
score.student_id,
student.sname
from
score
left join student on score.student_id = student.sid
where
student_id != 2
and course_id in (
select
course_id
from
score
where
student_id = 2
)
group by
student_id
having
count(1) = (
select
count(1)
from
score
where
student_id = 2
)
- 删除学习叶平老师课的score表记录
delete
from
score
where
course_id in (
select
cid
from
course
left join teacher on course.teacher_id = teacher.tid
where
teacher. name = '叶平老师'
)
- 向t1表中插入一些记录，这些记录要求符合以下条件：1. 没有上过课程编号为2的同学学号 2. 插入课程编号为2的平均成绩 -> 由于insert 支持 inset into tb1(xx,xx) select x1,x2 from tb2; 的写法，所以可以直接将筛选到的数据插入表中
insert into t1 (sid, avg) select
student_id,
(
select
avg(num)
from
score
where
course_id = 2
) as avg
from
score
where
student_id not in (
select
student_id
from
score
where
course_id in (2)
)
group by
student_id;
- 按平均成绩从高到低，显示所有学生的生物、物理、体育、美术四门的课程成绩，按如下形式显示: 学生ID,语文,数学,英语,课程数,平均分
select
student_id,
(select num from score as s2 where s2.student_id = s1.student_id and course_id = 1) as '生物',
(select num from score as s2 where s2.student_id = s1.student_id and course_id = 2) as '物理',
(select num from score as s2 where s2.student_id = s1.student_id and course_id = 3) as '体育',
(select num from score as s2 where s2.student_id = s1.student_id and course_id = 4) as '美术',
(select count(1) from score as s2 where s2.student_id = s1.student_id group by student_id) as '课程数',
(select avg(num) from score as s2 where s2.student_id = s1.student_id group by student_id) as '平均分'
from
score as s1
group by
student_id
order by
平均分 desc;
- 查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分
select course_id, max(num) as '最高分', min(num) as '最低分' from score group by course_id;
- 按各科平均成绩从低到高和及格率的百分数从高到低顺序 -> （通过 course_id 进行分组 -> 统计的合格人数 -> 将合格人数除以该科目的总人数得到及格率）
select
course_id,
avg(num) as avg,
sum(case when num>= 60 then 1 else 0 end) / count(1) as percent
from
score
group by
course_id;
- 课程平均分从高到低显示(现实任课老师) -> (将成绩表，课程表，教师表关联起来 -> 通过 course_id 进行分组查询平均值然后进行排序)
select
teacher.tname,
course.cname,
avg(
if (isnull(score.num), 0, score.num) -- 如果 score.num 得到值是 null 那么就返回一个0去计算平均值，反之使用原本的 score.num 去计算平均值
) as '平均分'
from
score
left join course on score.course_id = course.cid
left join teacher on course.teacher_id = teacher.tid
group by
course_id
order by
平均分 desc;
- 查询各科成绩前三名的记录: 不考虑成绩并列情况 -> (通过排序+分页查询出各科的第一名成绩和第三名成绩追加到成绩表每一条数据后面 -> 将成绩表查询出来的所有数据作为临时表，因为select语句在进行条件筛选的时候只能使用自己表内的字段，而通过select语句额外添加的字段是无法获取到的该字段的数据，所以要将成绩表查询出来的所有数据作为临时表然后再进行条件的筛选)
select
*
from
(
select
sid,
course_id,
num,
(select num from score as s2 where s1.course_id = s2.course_id order by num desc limit 0,1) as first_num,
(select num from score as s2 where s1.course_id = s2.course_id order by num desc limit 3,1) as second_num
from
score as s1
) as T
where num <= first_num and num >= second_num order by course_id asc, num desc;
- 查询每门课程被选修的学生数 -> (将成绩表和学生表关联起来 -> 通过 course_id 进行分组查询统计出每门课的选修人数)
select
course.cname as '课程名称',
count(1) as '学生人数'
from
score
left join course on score.course_id = course.cid
group by
course_id;
- 查询出只选修了一门课程的全部学生的学号和姓名 -> (将成绩表和学生表关联起来 -> 通过 student_id 进行分组查询统计每个学生的选课数 -> 筛选出选课数等于1的学生信息)
select
score.student_id,
student.sname
from
score
left join student on score.student_id = student.sid
group by
student_id
having
count(student_id) = 1;
- 查询男生、女生的人数
select gender, count(1) from student group by gender;
- 查询姓“张”的学生名单
select * from student where sname like '张%'
- 查询同名同姓学生名单，并统计同名人数
select sname,count(1) from student group by sname having count(1)>=2;
- 查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列 -> (将成绩表和课程表关联起来，通过 course_id 进行分组统计出每科的平均值 -> 对平均值进行排序)
select
course.cname,
avg(num) as avg_num
from
score
left join course on score.course_id = course.cid
group by
course_id
order by
avg_num asc,
score.course_id desc;
- 查询平均成绩大于85的所有学生的学号、姓名和平均成绩 -> (将成绩表和学生表关联起来 -> 通过 student_id 进行分组统计出每个学生的平均，然后筛选出平均分高于85的学生)
select
score.student_id,
student.sname,
avg(
if (isnull(score.num), 0, score.num)
) as avg
from
score
left join student on score.student_id = student.sid
group by
student_id
having
avg > 85;
- 查询课程名称为生物，且分数低于60的学生姓名和分数
select
student.sname,
score.num
from
score
left join course on score.course_id = course.cid
left join student on score.student_id = student.sid
where
num < 60
and cname = '生物';
- 查询课程编号为003且课程成绩在80分以上的学生的学号和姓名
select
score.student_id,
student.sname
from
score
left join student on score.student_id = student.sid
where
score.course_id = 3
and score.num > 80;
- 求选了课程的学生人数
# 写法一
select count(distinct student_id) as '人数' from score
# 写法二
select count(1) as '人数' from (select student_id,count(1) from score group by student_id) as A;
- 查询选修李平老师所授课程的学生中，成绩最高的学生姓名及其成绩 -> (查询李平老师所教的课程id -> 将成绩表和学生表关联起来，查询学了李平老师课的学生 -> 通过排序+分页获取到成绩最高的学生)
select
student.sid,
student.sname,
score.num
from
score
left join student on score.student_id = student.sid
where
course_id in (
select
cid
from
course
left join teacher on course.teacher_id = teacher.tid
where
tname = '李平老师'
)
order by
num desc
limit 0, 1
- 查询各个课程及相应的选修人数
select
course.cid,
course.cname,
count(1) as '人数'
from
score
left join course on score.course_id = course.cid
group by
score.course_id;
- 查询不同课程但成绩相同的学生的学号、课程号、学生成绩 -> 关联两个相同的表从而进行判断
select distinct
s1.course_id,
s1.num,
s2.course_id,
s2.num
from
score as s1,
score as s2
where
s1.num = s2.num and s1.course_id != s2.course_id
order by
s1.course_id asc;
- 检索至少选修两门课程的学生学号
select student_id, count(1) from score group by student_id having count(1) > 1;
- 查询全部学生都选修的课程的课程号和课程名
select
score.course_id,
course.cname,
count(1) as '选课人数'
from
score
left join course on score.course_id = course.cid
group by
score.course_id
having
选课人数 = (
select
count(1)
from
student
)
- 查询没学过叶平老师讲授的任一门课程的学生姓名
select
sname
from
score
left join student on score.student_id = student.sid
where
score.course_id not in (
select
cid
from
course
left join teacher on course.teacher_id = teacher.tid
where
teacher.tname = '李平老师'
)
group by
score.student_id;
- 查询两门以上不及格课程的同学的学号
select student_id from score where num < 60 group by student_id having count(1) > 1
- 检索课程编号为4分数小于60的同学学号，并且按分数降序排列
select student_id, num from score where course_id = 4 and num < 60 order by num desc;
- 删除学生编号为2的同学的课程编号为1的成绩
delete from score where course_id = 1 and student_id = 2
MySQL的介绍 →