查询练习
建表，插入数据 新建一个查询用的数据库:selectTest CREATE DATABASE selectTest; 选择该数据库: USE selectTest;
学生表: student 学号 姓名 性别 出生日期 所在班级
CREATE TABLE student(
s_no VARCHAR(20) PRIMARY KEY COMMENT'学生学号',
s_name VARCHAR(20) NOT NULL COMMENT'学生姓名 不能为空',
s_sex VARCHAR(10) NOT NULL COMMENT'学生性别',
s_birthday DATETIME COMMENT'学生生日',
s_class VARCHAR(20) COMMENT'学生所在的班级'
)ENGINE=InnoDB CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;
教师表 teacher 教师编号 教师名字 教师性别 出生日期 职称 所在部门
CREATE TABLE teacher(
t_no VARCHAR(20) PRIMARY KEY COMMENT'教师编号',
t_name VARCHAR(20) NOT NULL COMMENT'教师姓名',
t_sex VARCHAR(20) NOT NULL COMMENT'教师性别',
t_birthday DATETIME COMMENT'教师生日',
t_rof VARCHAR(20) NOT NULL COMMENT'教师职称',
t_depart VARCHAR(20) NOT NULL COMMENT'教师所在的部门'
)ENGINE=InnoDB CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;
课程表: course 课程号 课程课程名称 教师编号
CREATE TABLE course(
c_no VARCHAR(20) PRIMARY KEY COMMENT'课程号',
c_name VARCHAR(20) NOT NULL COMMENT'课程名称',
t_no VARCHAR(20) NOT NULL COMMENT'教师编号 外键关联teacher表',
FOREIGN KEY(t_no) references teacher(t_no)
)ENGINE=InnoDB CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;
成绩表 srore 学号 课程号 成绩 注意:视频中原先只有一个主键s_no ,后来修改了
CREATE TABLE score (
s_no VARCHAR(20) NOT NULL COMMENT'成绩表的编号 依赖学生学号',
c_no VARCHAR(20) NOT NULL COMMENT'课程号 依赖于课程表中的c_id',
sc_degree decimal,
foreign key(s_no) references student(s_no),
foreign key(c_no) references course(c_no),
PRIMARY KEY(s_no,c_no)
)ENGINE=InnoDB CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;
查看创建的表以及架构
SHOW TABLES;
+----------------------+
| Tables_in_selecttest |
+----------------------+
| course |
| score |
| student |
| teacher |
+----------------------+
查看student表结构 DESCRIBE student;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| s_no | varchar(20) | NO | PRI | NULL | |
| s_name | varchar(20) | NO | | NULL | |
| s_sex | varchar(10) | NO | | NULL | |
| s_birthday | datetime | YES | | NULL | |
| s_class | varchar(20) | YES | | NULL | |
+------------+-------------+------+-----+---------+-------+
查看teacher表结构
DESCRIBE teacher;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| t_no | varchar(20) | NO | PRI | NULL | |
| t_name | varchar(20) | NO | | NULL | |
| t_sex | varchar(20) | NO | | NULL | |
| t_birthday | datetime | YES | | NULL | |
| t_rof | varchar(20) | NO | | NULL | |
| t_depart | varchar(20) | NO | | NULL | |
+------------+-------------+------+-----+---------+-------+
查看course表结构
DESCRIBE course;
+--------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| c_no | varchar(20) | NO | PRI | NULL | |
| c_name | varchar(20) | NO | | NULL | |
| t_no | varchar(20) | NO | MUL | NULL | |
+--------+-------------+------+-----+---------+-------+
查看score表结构
DESCRIBE score;
+-----------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------+------+-----+---------+-------+
| s_no | varchar(20) | NO | PRI | NULL | |
| c_no | varchar(20) | NO | MUL | NULL | |
| sc_degree | decimal(10,0) | YES | | NULL | |
+-----------+---------------+------+-----+---------+-------+
向表中添加数据
--学生表数据
INSERT INTO student VALUES('101','曾华','男','1977-09-01','95033');
INSERT INTO student VALUES('102','匡明','男','1975-10-02','95031');
INSERT INTO student VALUES('103','王丽','女','1976-01-23','95033');
INSERT INTO student VALUES('104','李军','男','1976-02-20','95033');
INSERT INTO student VALUES('105','王芳','女','1975-02-10','95031');
INSERT INTO student VALUES('106','陆军','男','1974-06-03','95031');
INSERT INTO student VALUES('107','王尼玛','男','1976-02-20','95033');
INSERT INTO student VALUES('108','张全蛋','男','1975-02-10','95031');
INSERT INTO student VALUES('109','赵铁柱','男','1974-06-03','95031');
--教师表数据
INSERT INTO teacher VALUES('804','李诚','男','1958-12-02','副教授','计算机系');
INSERT INTO teacher VALUES('856','张旭','男','1969-03-12','讲师','电子工程系');
INSERT INTO teacher VALUES('825','王萍','女','1972-05-05','助教','计算机系');
INSERT INTO teacher VALUES('831','刘冰','女','1977-08-14','助教','电子工程系');
--添加课程表
INSERT INTO course VALUES('3-105','计算机导论','825');
INSERT INTO course VALUES('3-245','操作系统','804');
INSERT INTO course VALUES('6-166','数字电路','856');
INSERT INTO course VALUES('9-888','高等数学','831');
--添加成绩表
INSERT INTO score VALUES('103','3-245','86');
INSERT INTO score VALUES('105','3-245','75');
INSERT INTO score VALUES('109','3-245','68');
INSERT INTO score VALUES('103','3-105','92');
INSERT INTO score VALUES('105','3-105','88');
INSERT INTO score VALUES('109','3-105','76');
INSERT INTO score VALUES('103','6-166','85');
INSERT INTO score VALUES('105','6-166','79');
INSERT INTO score VALUES('109','6-166','81');
几张表的数据展现
SELECT * FROM student;
+------+--------+-------+---------------------+---------+
| s_no | s_name | s_sex | s_birthday | s_class |
+------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+------+--------+-------+---------------------+---------+
teacher SELECT * FROM teacher;
+------+--------+-------+---------------------+--------+------------+
| t_no | t_name | t_sex | t_birthday | t_rof | t_depart |
+------+--------+-------+---------------------+--------+------------+
| 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机机系 |
| 831 | 刘冰 | 女 | 1977-08-14 00:00:00 | 助教 | 电子工程系 |
| 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
+------+--------+-------+---------------------+--------+------------+
score SELECT * FROM score;
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+------+-------+-----------+
course SELECT * FROM course;
+-------+------------+------+
| c_no | c_name | t_no |
+-------+------------+------+
| 3-105 | 计算机导论 | 825 |
| 3-245 | 操作系统 | 804 |
| 6-166 | 数字电路 | 856 |
| 9-888 | 高等数学 | 831 |
+-------+------------+------+
select * from student;
select s_name,s_sex,s_class from student;
1.筛选出老师属于哪些专业，不能重复
select distinct t_depart from teacher;
mysql> select distinct t_depart from teacher;
+-----------------+
| t_depart |
+-----------------+
| 计算机系 |
| 电子工程系 |
+-----------------+
4.筛选出score表中60分到80分的学生
select * from score where sc_degree between 60 and 80;
或者
select * from score where sc_degree > 60 and sc_degree <80;
mysql> select * from score where sc_degree between 60 and 80;
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
+------+-------+-----------+
4 rows in set (0.00 sec)
5.筛选得到85或86或87分的同学
select * from score where sc_degree = 85 or sc_degree = 86 or sc_degree = 87;
select * from score where sc_degree in(85,86,87);
mysql> select * from score where sc_degree = 85 or sc_degree = 86 or sc_degree = 87;
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
+------+-------+-----------+
2 rows in set (0.00 sec)
6.找到学生，要求班级为95031号或者女生
select * from student where s_class = 95031 or s_sex = '女';
mysql> select * from student where s_class = 95031 or s_sex = '女';
+------+-----------+-------+---------------------+---------+
| s_no | s_name | s_sex | s_birthday | s_class |
+------+-----------+-------+---------------------+---------+
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+------+-----------+-------+---------------------+---------+
6 rows in set (0.00 sec)
升降序练习（order by,asc升序 desc）
7.以班级号码倒叙排列所有学生
select * from student order by s_class desc;
mysql> select * from student order by s_class desc;
+------+-----------+-------+---------------------+---------+
| s_no | s_name | s_sex | s_birthday | s_class |
+------+-----------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+------+-----------+-------+---------------------+---------+
9 rows in set (0.00 sec)
8.对于成绩，以升序排列班级号码，倒叙排列成绩
select * from score order by c_no asc,sc_degree desc;
mysql> select * from score order by c_no asc,sc_degree desc;
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-105 | 92 |
| 105 | 3-105 | 88 |
| 109 | 3-105 | 76 |
| 103 | 3-245 | 86 |
| 105 | 3-245 | 75 |
| 109 | 3-245 | 68 |
| 103 | 6-166 | 85 |
| 109 | 6-166 | 81 |
| 105 | 6-166 | 79 |
+------+-------+-----------+
9 rows in set (0.00 sec)
统计数量（count）
9.统计班级号为95033的同学总共有多少
select count(*) from student where s_class='95033';
mysql> select count(*) from student where s_class='95033';
+----------+
| count(*) |
+----------+
| 4 |
+----------+
1 row in set (0.00 sec)
子查询
10.求最高分学生的学号和课程编号，max()
select s_no,c_no from score where sc_degree = (select max(sc_degree) from score);
mysql> select s_no,c_no from score where sc_degree = (select max(sc_degree) from score);
+------+-------+
| s_no | c_no |
+------+-------+
| 103 | 3-105 |
+------+-------+
1 row in set (0.00 sec)
切片（limit）
# 展示成绩表中，倒叙排列成绩，只显示学号和班级号，最后切片，只显示第一个
select s_no,c_no from score where sc_degree order by sc_degree desc limit 0,1;
mysql> select s_no,c_no from score where sc_degree order by sc_degree desc limit 0,1;
+------+-------+
| s_no | c_no |
+------+-------+
| 103 | 3-105 |
+------+-------+
1 row in set (0.00 sec)
计算平均成绩（avg,group by）
11.查询每门课的平均成绩
select c_no,avg(sc_degree) from score group by c_no;
mysql> select c_no,avg(sc_degree) from score group by c_no;
+-------+----------------+
| c_no | avg(sc_degree) |
+-------+----------------+
| 3-105 | 85.3333 |
| 3-245 | 76.3333 |
| 6-166 | 81.6667 |
+-------+----------------+
3 rows in set (0.00 sec)
分组条件及模糊查询（group by having,like）
12.查询score表中至少有两名学生选修并以3开头的课程的平均分数
select c_no,avg(sc_degree),count(c_no) from score group by c_no
having count(c_no) >2 and c_no like '3%';
mysql> select c_no,avg(sc_degree),count(c_no) from score group by c_no
having count(c_no) >2 and c_no like '3%';
+-------+----------------+-------------+
| c_no | avg(sc_degree) | count(c_no) |
+-------+----------------+-------------+
| 3-105 | 85.3333 | 3 |
| 3-245 | 76.3333 | 3 |
+-------+----------------+-------------+
2 rows in set (0.00 sec)
范围查询（between and）
13.查询分数大于70，小于90的s_no列
select s_no,sc_degree from score where sc_degree >70 and sc_degree <90;
select s_no,sc_degree from score where sc_degree between 70 and 90;
mysql> select s_no,sc_degree from score where sc_degree between 70 and 90;
+------+-----------+
| s_no | sc_degree |
+------+-----------+
| 103 | 86 |
| 103 | 85 |
| 105 | 88 |
| 105 | 75 |
| 105 | 79 |
| 109 | 76 |
| 109 | 81 |
+------+-----------+
7 rows in set (0.00 sec)
多表查询(寻找相同条件)
14. 查询所有学生的s_name\c_no\sc_degree
select s_name,c_no,sc_degree from student,score where student.s_no=score.s_no;
15.查询所有学生的s_no, c_name, sc_degree列
select s_no,c_name,sc_degree from score,course where score.c_no=course.c_no;
mysql> select s_no,c_name,sc_degree from score,course where score.c_no=course.c_no;
+------+------------+-----------+
| s_no | c_name | sc_degree |
+------+------------+-----------+
| 103 | 计算机导论 | 92 |
| 103 | 操作系统 | 86 |
| 103 | 数字电路 | 85 |
| 105 | 计算机导论 | 88 |
| 105 | 操作系统 | 75 |
| 105 | 数字电路 | 79 |
| 109 | 计算机导论 | 76 |
| 109 | 操作系统 | 68 |
| 109 | 数字电路 | 81 |
+------+------------+-----------+
9 rows in set (0.03 sec)
子查询加分组求平均分(in )
17. 查询班级是'95031'班学生每门课的平均分
select avg(sc_degree) from score
where s_no in (select s_no from student where s_class='95031') group by c_no;
子查询深入
18. 查询选修"3-105"课程的成绩高于'109'分同学'3-105'成绩 的所有同学的记录
(在大家都在选修3-105的背景下 查询 所有 分数 比 学号为"109"还要高的学生信息)
select * from score where c_no='3-105' and sc_degree >
(select sc_degree from score where c_no='3-105' and s_no='109');
mysql> select * from score where c_no='3-105' and sc_degree >
-> (select sc_degree from score where c_no='3-105' and s_no='109');
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-105 | 92 |
| 105 | 3-105 | 88 |
+------+-------+-----------+
2 rows in set (0.00 sec)
19.查询成绩高于学号为'109',课程号为'3-105'的成绩的所有记录
(不管哪门课，只要比那个分数高就行)
select * from score where sc_degree >
(select sc_degree from score where c_no='3-105' and s_no='109');
mysql> select * from score where sc_degree > (select sc_degree from score where c_no='3-105' and s_no='109');
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 105 | 3-105 | 88 |
| 105 | 6-166 | 79 |
| 109 | 6-166 | 81 |
+------+-------+-----------+
6 rows in set (0.00 sec)
年份函数(year)
20.查询所有学号为108.101的同学同年出生的所有学生的s_no,s_name和s_birthday
select s_no,s_name,s_birthday from student
where year(s_birthday) in (select year(s_birthday) from student where s_no in (101,108));
mysql> select s_no,s_name,s_birthday from student
-> where year(s_birthday) in (select year(s_birthday) from student where s_no in (101,108));
+------+--------+---------------------+
| s_no | s_name | s_birthday |
+------+--------+---------------------+
| 101 | 曾华 | 1977-09-01 00:00:00 |
| 102 | 匡明 | 1975-10-02 00:00:00 |
| 105 | 王芳 | 1975-02-10 00:00:00 |
| 108 | 张全蛋 | 1975-02-10 00:00:00 |
+------+--------+---------------------+
嵌套子查询
21. 查询张旭老师上的课的学生的成绩
select t_no from teacher where t_name = '张旭';
select c_no from class where t_no = (select t_no from teacher where t_name = '张旭');
select * from score where c_no =(select c_no from course where t_no = (select t_no from teacher where t_name = '张旭'));
in的使用
23.查询班级号为95033,95031的学生，并且倒叙排序
select * from student where s_class in (95033,95031) order by s_class;
mysql> select * from student where s_class in (95033,95031) order by s_class;
+------+--------+-------+---------------------+---------+
| s_no | s_name | s_sex | s_birthday | s_class |
+------+--------+-------+---------------------+---------+
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
+------+--------+-------+---------------------+---------+
9 rows in set (0.00 sec)
24. 查询存在85分以上成绩的课程c_no
select c_no from score where sc_degree >85;
mysql> select c_no from score where sc_degree >85;
+-------+
| c_no |
+-------+
| 3-105 |
| 3-105 |
| 3-105 |
| 3-245 |
| 3-105 |
| 3-105 |
+-------+
6 rows in set (0.00 sec)
综合使用
25.查出所有'计算机系' 教师所教课程的成绩表
select t_no from teacher where t_depart='计算机系';
select c_no from course where t_no in (select t_no from teacher where t_depart='计算机系');
select * from score where c_no in(select c_no from course where t_no in (select t_no from teacher where t_depart='计算机系'));
mysql> select * from score where c_no in(select c_no from course where t_no in (select t_no from teacher where t_depart='计算机系'));
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-245 | 86 |
| 105 | 3-245 | 75 |
| 109 | 3-245 | 68 |
| 101 | 3-105 | 90 |
| 102 | 3-105 | 91 |
| 103 | 3-105 | 92 |
| 104 | 3-105 | 89 |
| 105 | 3-105 | 88 |
| 109 | 3-105 | 76 |
+------+-------+-----------+
9 rows in set (0.00 sec)
求并集操作(union)
26.查询'计算机系'与'电子工程系' 不同职称的教师的t_name和rof
select * from teacher where t_depart='计算机系'
and t_rof not in (select t_rof from teacher where t_depart='电子工程系')
union
select * from teacher where t_depart='电子工程系'
and t_rof not in (select t_rof from teacher where t_depart='计算机系');
mysql> select * from teacher where t_depart='计算机系' and t_rof not in (select t_rof from teacher where t_depart='电子 工程系')
-> union
-> select * from teacher where t_depart='电子工程系' and t_rof not in (select t_rof from teacher where t_depart='计 算机系');
+------+--------+-------+---------------------+--------+------------+
| t_no | t_name | t_sex | t_birthday | t_rof | t_depart |
+------+--------+-------+---------------------+--------+------------+
| 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
+------+--------+-------+---------------------+--------+------------+
2 rows in set (0.00 sec)
严格正确版：
select t_name,t_rof from teacher where t_depart='计算机系'
and t_rof not in (select t_rof from teacher where t_depart='电子工程系')
union
select t_name,t_rof from teacher where t_depart='电子工程系'
and t_rof not in (select t_rof from teacher where t_depart='计算机系');
+--------+--------+
| t_name | t_rof |
+--------+--------+
| 李诚 | 副教授 |
| 张旭 | 讲师 |
+--------+--------+
2 rows in set (0.00 sec)
多个值比较多个值：至少（any）
27, 查询选修编号为"3-105"课程且成绩至少高于选修编号为'3-245'同学的c_no,s_no和sc_degree,并且按照sc_degree从高到地次序排序
select c_no,s_no,sc_degree from score where c_no='3-105' and sc_degree > any(select sc_degree from score where c_no='3-245') order by sc_degree desc;
+-------+------+-----------+
| c_no | s_no | sc_degree |
+-------+------+-----------+
| 3-105 | 103 | 92 |
| 3-105 | 102 | 91 |
| 3-105 | 101 | 90 |
| 3-105 | 104 | 89 |
| 3-105 | 105 | 88 |
| 3-105 | 109 | 76 |
+-------+------+-----------+
6 rows in set (0.00 sec)
多个值比较多个值：所有（all）
28.查询选修编号为"3-105"且成绩高于选修编号为"3-245"课程的同学c_no.s_no和sc_degree
select c_no,s_no,sc_degree from score where c_no='3-105' and sc_degree > all(select sc_degree from score where c_no='3-245');
+-------+------+-----------+
| c_no | s_no | sc_degree |
+-------+------+-----------+
| 3-105 | 101 | 90 |
| 3-105 | 102 | 91 |
| 3-105 | 103 | 92 |
| 3-105 | 104 | 89 |
| 3-105 | 105 | 88 |
+-------+------+-----------+
5 rows in set (0.00 sec)
使用别名(as)
29.查询所有教师和同学的 name ,sex, birthday
select s_name as name,s_sex as sex,s_birthday as birthday from student
union
select t_name as name,t_sex as sex,t_birthday as birthday from teacher;
mysql> select s_name as name,s_sex as sex,s_birthday as birthday from student
-> union
-> select t_name as name,t_sex as sex,t_birthday as birthday from teacher;
+--------+-----+---------------------+
| name | sex | birthday |
+--------+-----+---------------------+
| 曾华 | 男 | 1977-09-01 00:00:00 |
| 匡明 | 男 | 1975-10-02 00:00:00 |
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 李军 | 男 | 1976-02-20 00:00:00 |
| 王芳 | 女 | 1975-02-10 00:00:00 |
| 陆军 | 男 | 1974-06-03 00:00:00 |
| 王尼玛 | 男 | 1976-02-20 00:00:00 |
| 张全蛋 | 男 | 1975-02-10 00:00:00 |
| 赵铁柱 | 男 | 1974-06-03 00:00:00 |
| 李诚 | 男 | 1958-12-02 00:00:00 |
| 王萍 | 女 | 1972-05-05 00:00:00 |
| 刘冰 | 女 | 1977-08-14 00:00:00 |
| 张旭 | 男 | 1969-03-12 00:00:00 |
+--------+-----+---------------------+
30.查询所有'女'教师和'女'学生的name,sex,birthday
select s_name as name,s_sex as sex,s_birthday as birthday from student where s_sex='女'
union
select t_name as name,t_sex as sex,t_birthday as birthday from teacher where t_sex='女';
+------+-----+---------------------+
| name | sex | birthday |
+------+-----+---------------------+
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 王芳 | 女 | 1975-02-10 00:00:00 |
| 王萍 | 女 | 1972-05-05 00:00:00 |
| 刘冰 | 女 | 1977-08-14 00:00:00 |
+------+-----+---------------------+
4 rows in set (0.00 sec)
复制表数据作条件查询(别名的使用)
31. 查询成绩比该课程平均成绩低的同学的成绩表
select * from score a where sc_degree < (select avg(sc_degree) from score b where a.c_no=b.c_no);
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+------+-------+-----------+
5 rows in set (0.01 sec)
32.查询所有任课教师的t_name 和 t_depart(要在分数表中可以查得到)
select t_name,t_depart from teacher where t_no in (select t_no from course);
+--------+------------+
| t_name | t_depart |
+--------+------------+
| 李诚 | 计算机系 |
| 王萍 | 计算机系 |
| 刘冰 | 电子工程系 |
| 张旭 | 电子工程系 |
+--------+------------+
4 rows in set (0.02 sec)
条件加分组查询
33.查出至少有2名男生的班号
select s_class from student group by s_class having count(s_sex='男')>1;
select s_class from student where s_sex='男' group by s_class having count(s_no)>1;
mysql> select s_class from student where s_sex='男' group by s_class having count(s_no)>1;
+---------+
| s_class |
+---------+
| 95033 |
| 95031 |
+---------+
2 rows in set (0.00 sec)
模糊查询取反(not like,%)
34. 查询student 表中不姓"王"的同学的记录
select * from student where s_name not like '王%';
+------+--------+-------+---------------------+---------+
| s_no | s_name | s_sex | s_birthday | s_class |
+------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+------+--------+-------+---------------------+---------+
6 rows in set (0.00 sec)
计算年龄大小(year(now()))
35. 查询student 中每个学生的姓名和年龄(当前时间 - 出生年份)
select s_name,year(now())-year(s_birthday) as age from student;
+--------+------+
| s_name | age |
+--------+------+
| 曾华 | 43 |
| 匡明 | 45 |
| 王丽 | 44 |
| 李军 | 44 |
| 王芳 | 45 |
| 陆军 | 46 |
| 王尼玛 | 44 |
| 张全蛋 | 45 |
| 赵铁柱 | 46 |
+--------+------+
最大值最小值（min,max）
36. 查询student中最大和最小的 s_birthday的值
select min(s_birthday),max(s_birthday) from student;
+---------------------+---------------------+
| min(s_birthday) | max(s_birthday) |
+---------------------+---------------------+
| 1974-06-03 00:00:00 | 1977-09-01 00:00:00 |
+---------------------+---------------------+
1 row in set (0.00 sec)
多字段排序
37. 以班级号和年龄从大到小的顺序查询student表中的全部记录
select * from student order by s_class desc and s_birthday;
+------+--------+-------+---------------------+---------+
| s_no | s_name | s_sex | s_birthday | s_class |
+------+--------+-------+---------------------+---------+
| 101 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 102 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 103 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 104 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 105 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
| 106 | 陆军 | 男 | 1974-06-03 00:00:00 | 95031 |
| 107 | 王尼玛 | 男 | 1976-02-20 00:00:00 | 95033 |
| 108 | 张全蛋 | 男 | 1975-02-10 00:00:00 | 95031 |
| 109 | 赵铁柱 | 男 | 1974-06-03 00:00:00 | 95031 |
+------+--------+-------+---------------------+---------+
9 rows in set (0.00 sec)
子查询练习
38. 查询"男"教师 及其所上的课
select t_no from teacher where t_sex='男';
select * from course where t_no in (select t_no from teacher where t_sex='男');
mysql> select * from course where t_no in (select t_no from teacher where t_sex='男');
+-------+----------+------+
| c_no | c_name | t_no |
+-------+----------+------+
| 3-245 | 操作系统 | 804 |
| 6-166 | 数字电路 | 856 |
+-------+----------+------+
2 rows in set (0.00 sec)
39.查询最高分同学的s_no c_no 和 sc_degree;
select max(sc_degree) from score;
select * from score where sc_degree =(select max(sc_degree) from score);
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 103 | 3-105 | 92 |
+------+-------+-----------+
1 row in set (0.00 sec)
40. 查询和"李军"同性别的所有同学的s_name
select s_name from student where s_sex = (select s_sex from student where s_name='李军');
mysql> select s_name from student where s_sex = (select s_sex from student where s_name='李军');
+--------+
| s_name |
+--------+
| 曾华 |
| 匡明 |
| 李军 |
| 陆军 |
| 王尼玛 |
| 张全蛋 |
| 赵铁柱 |
+--------+
7 rows in set (0.00 sec)
41.查询和"李军"同性别并且同班的所有同学的s_name
SELECT s_name, s_sex FROM student WHERE s_sex = (SELECT s_sex FROM student WHERE s_name = '李军') AND s_class = (SELECT s_class FROM student WHERE s_name = '李军');
+--------+
| s_name |
+--------+
| 曾华 |
| 李军 |
| 王尼玛 |
+--------+
3 rows in set (0.00 sec)
42. 查询所有选修'计算机导论'课程的'男'同学的成绩表
select c_no from course where c_name='计算机导论';
select s_no from student where s_sex='男'；
select * from score where s_no in (select s_no from student where s_sex='男') and
c_no in (select c_no from course where c_name='计算机导论');
+------+-------+-----------+
| s_no | c_no | sc_degree |
+------+-------+-----------+
| 101 | 3-105 | 90 |
| 102 | 3-105 | 91 |
| 104 | 3-105 | 89 |
| 109 | 3-105 | 76 |
+------+-------+-----------+
4 rows in set (0.00 sec)
连接查询
左外连接
左连接
全连接
两张表都没有出现交集的数据集
右连接
右外连接
内连接
连接查询案例
内连接（inner join …… on）
mysql> create table card(
-> id int,
-> name varchar(20)
-> );
insert into card values(1,'饭卡');
insert into card values(2,'建行卡');
insert into card values(3,'农行卡');
insert into card values(4,'工商卡');
insert into card values(5,'邮政卡');
mysql> create table person(
-> id int,
-> name varchar(20),
-> cardId int);
insert into person values(1,'张三',1);
insert into person values(2,'李四',3);
insert into person values(3,'王五',6);
person表:
mysql> select * from person;
+------+--------+--------+
| id | name | cardId |
+------+--------+--------+
| 1 | 张三 | 1 |
| 2 | 李四 | 3 |
| 3 | 王五 | 6 |
+------+--------+--------+
3 rows in set (0.00 sec)
card表:
mysql> select * from card;
+------+-----------+
| id | name |
+------+-----------+
| 1 | 饭卡 |
| 2 | 建行卡 |
| 3 | 农行卡 |
| 4 | 工商卡 |
| 5 | 邮政卡 |
+------+-----------+
5 rows in set (0.00 sec)
内连接查询
select * from person inner join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
+------+------+--------+------+--------+
2 rows in set (0.00 sec)
整个查询的执行过程如下:
- 从
person表中选取所有记录 - 对于每个
person记录,查找card表中id字段与person.cardId相匹配的记录 - 将匹配的
person和card记录组合成一条结果记录返回
外连接
左外连接(left join ...... on)
左外连接会把左边的表的数据全部取出来 ，右边表如果没有就用NULL补上
mysql> select * from person left join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| 3 | 王五 | 6 | NULL | NULL |
+------+------+--------+------+--------+
3 rows in set (0.00 sec)
整个查询的执行过程如下:
- 从
person表中选取所有记录 - 对于每个
person记录,查找card表中id字段与person.cardId相匹配的记录 - 将匹配的
person和card记录组合成一条结果记录返回 - 对于无法匹配的
person记录,用NULL填充card表的字段
右外连接(right join ...... on)
右外连接会把左边的表的数据全部取出来，左边表如果没有就用NULL补上
mysql> select * from person right join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| NULL | NULL | NULL | 2 | 建行卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| NULL | NULL | NULL | 4 | 工商卡 |
| NULL | NULL | NULL | 5 | 邮政卡 |
+------+------+--------+------+--------+
5 rows in set (0.00 sec)
整个查询的执行过程如下:
- 从
card表中选取所有记录 - 对于每个
card记录,查找person表中cardId字段与card.id相匹配的记录 - 将匹配的
person和card记录组合成一条结果记录返回 - 对于无法匹配的
card记录,用NULL填充person表的字段
全连接（full join）
select * from person full join card on person.cardId=card.id;
mysql不支持全连接，换一种方式表达
select * from person left join card on person.cardId=card.id union select * from person right join card on person.cardId=card.id;
+------+------+--------+------+--------+
| id | name | cardId | id | name |
+------+------+--------+------+--------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| 3 | 王五 | 6 | NULL | NULL |
| NULL | NULL | NULL | 2 | 建行卡 |
| NULL | NULL | NULL | 4 | 工商卡 |
| NULL | NULL | NULL | 5 | 邮政卡 |
+------+------+--------+------+--------+
6 rows in set (0.00 sec)
整个查询的执行过程如下:
- 从
person表和card表中选取所有记录 - 对于每个
person记录,查找card表中id字段与person.cardId相匹配的记录 - 对于每个
card记录,查找person表中cardId字段与card.id相匹配的记录 - 将匹配的
person和card记录组合成一条结果记录返回 - 对于无法匹配的记录,用
NULL填充相应的字段