9 MySQL

1多表查询：
2    http://www.cnblogs.com/linhaifeng/articles/7267596.html
3    1.多表连接查询
4    2.符合条件连接查询
5    3.子查询

一、准备表

1#建表
2create table department(
3id int,
4name varchar(20) 
5);
6
7create table employee(
8id int primary key auto_increment,
9name varchar(20),
10sex enum('male','female') not null default 'male',
11age int,
12dep_id int
13);
14
15#插入数据
16insert into department values
17(200,'技术'),
18(201,'人力资源'),
19(202,'销售'),
20(203,'运营');
21
22insert into employee(name,sex,age,dep_id) values
23('egon','male',18,200),
24('alex','female',48,201),
25('wupeiqi','male',38,201),
26('yuanhao','female',28,202),
27('liwenzhou','male',18,200),
28('jingliyang','female',18,204)
29;
30
31
32#查看表结构和数据
33mysql> desc department;
34+-------+-------------+------+-----+---------+-------+
35| Field | Type | Null | Key | Default | Extra |
36+-------+-------------+------+-----+---------+-------+
37| id | int(11) | YES | | NULL | |
38| name | varchar(20) | YES | | NULL | |
39+-------+-------------+------+-----+---------+-------+
40
41mysql> desc employee;
42+--------+-----------------------+------+-----+---------+----------------+
43| Field | Type | Null | Key | Default | Extra |
44+--------+-----------------------+------+-----+---------+----------------+
45| id | int(11) | NO | PRI | NULL | auto_increment |
46| name | varchar(20) | YES | | NULL | |
47| sex | enum('male','female') | NO | | male | |
48| age | int(11) | YES | | NULL | |
49| dep_id | int(11) | YES | | NULL | |
50+--------+-----------------------+------+-----+---------+----------------+
51
52mysql> select * from department;
53+------+--------------+
54| id | name |
55+------+--------------+
56| 200 | 技术 |
57| 201 | 人力资源 |
58| 202 | 销售 |
59| 203 | 运营 |
60+------+--------------+
61
62mysql> select * from employee;
63+----+------------+--------+------+--------+
64| id | name | sex | age | dep_id |
65+----+------------+--------+------+--------+
66| 1 | egon | male | 18 | 200 |
67| 2 | alex | female | 48 | 201 |
68| 3 | wupeiqi | male | 38 | 201 |
69| 4 | yuanhao | female | 28 | 202 |
70| 5 | liwenzhou | male | 18 | 200 |
71| 6 | jingliyang | female | 18 | 204 |
72+----+------------+--------+------+--------+
73
74表department与employee

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二、多表连接查询

1#重点：外链接语法
2
3SELECT 字段列表
4    FROM 表1 INNER|LEFT|RIGHT JOIN 表2
5    ON 表1.字段 = 表2.字段;

1 交叉连接：不适用任何匹配条件。生成笛卡尔积

1mysql> select * from employee,department;
2+----+------------+--------+------+--------+------+--------------+
3| id | name       | sex    | age  | dep_id | id   | name         |
4+----+------------+--------+------+--------+------+--------------+
5|  1 | egon       | male   |   18 |    200 |  200 | 技术         |
6|  1 | egon       | male   |   18 |    200 |  201 | 人力资源     |
7|  1 | egon       | male   |   18 |    200 |  202 | 销售         |
8|  1 | egon       | male   |   18 |    200 |  203 | 运营         |
9|  2 | alex       | female |   48 |    201 |  200 | 技术         |
10|  2 | alex       | female |   48 |    201 |  201 | 人力资源     |
11|  2 | alex       | female |   48 |    201 |  202 | 销售         |
12|  2 | alex       | female |   48 |    201 |  203 | 运营         |
13|  3 | wupeiqi    | male   |   38 |    201 |  200 | 技术         |
14|  3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
15|  3 | wupeiqi    | male   |   38 |    201 |  202 | 销售         |
16|  3 | wupeiqi    | male   |   38 |    201 |  203 | 运营         |
17|  4 | yuanhao    | female |   28 |    202 |  200 | 技术         |
18|  4 | yuanhao    | female |   28 |    202 |  201 | 人力资源     |
19|  4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
20|  4 | yuanhao    | female |   28 |    202 |  203 | 运营         |
21|  5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
22|  5 | liwenzhou  | male   |   18 |    200 |  201 | 人力资源     |
23|  5 | liwenzhou  | male   |   18 |    200 |  202 | 销售         |
24|  5 | liwenzhou  | male   |   18 |    200 |  203 | 运营         |
25|  6 | jingliyang | female |   18 |    204 |  200 | 技术         |
26|  6 | jingliyang | female |   18 |    204 |  201 | 人力资源     |
27|  6 | jingliyang | female |   18 |    204 |  202 | 销售         |
28|  6 | jingliyang | female |   18 |    204 |  203 | 运营         |
29+----+------------+--------+------+--------+------+--------------+

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1内连接：只取两张表的共同部分
2select * from employee inner join department on employee.dep_id = department.id ;
3
4左连接:在内连接的基础上保留左表的记录
5select * from employee left join department on employee.dep_id = department.id ;
6
7右连接：在内连接的基础上保留右表的记录
8select * from employee right join department on employee.dep_id = department.id ;
9
10全外连接：在内连接的基础上保留左右两表没有对应关系的记录
11select * from employee full join department on employee.dep_id = department.id ;
12
13
14select * from employee left join department on employee.dep_id = department.id
15union
16select * from employee right join department on employee.dep_id = department.id ;

2 内连接：只连接匹配的行

1#找两张表共有的部分，相当于利用条件从笛卡尔积结果中筛选出了正确的结果
2#department没有204这个部门，因而employee表中关于204这条员工信息没有匹配出来

1mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee inner join department on employee.dep_id=department.id; 
2+----+-----------+------+--------+--------------+
3| id | name      | age  | sex    | name         |
4+----+-----------+------+--------+--------------+
5|  1 | egon      |   18 | male   | 技术         |
6|  2 | alex      |   48 | female | 人力资源     |
7|  3 | wupeiqi   |   38 | male   | 人力资源     |
8|  4 | yuanhao   |   28 | female | 销售         |
9|  5 | liwenzhou |   18 | male   | 技术         |
10+----+-----------+------+--------+--------------+
11
12#上述sql等同于
13mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id=department.id;

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3 外链接之左连接：优先显示左表全部记录

1#以左表为准，即找出所有员工信息，当然包括没有部门的员工
2#本质就是：在内连接的基础上增加左边有右边没有的结果

1mysql> select employee.id,employee.name,department.name as depart_name from employee left join department on employee.dep_id=department.id;
2+----+------------+--------------+
3| id | name       | depart_name  |
4+----+------------+--------------+
5|  1 | egon       | 技术         |
6|  5 | liwenzhou  | 技术         |
7|  2 | alex       | 人力资源     |
8|  3 | wupeiqi    | 人力资源     |
9|  4 | yuanhao    | 销售         |
10|  6 | jingliyang | NULL         |
11+----+------------+--------------+

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4 外链接之右连接：优先显示右表全部记录

1#以右表为准，即找出所有部门信息，包括没有员工的部门
2#本质就是：在内连接的基础上增加右边有左边没有的结果

1mysql> select employee.id,employee.name,department.name as depart_name from employee right join department on employee.dep_id=department.id;
2+------+-----------+--------------+
3| id   | name      | depart_name  |
4+------+-----------+--------------+
5|    1 | egon      | 技术         |
6|    2 | alex      | 人力资源     |
7|    3 | wupeiqi   | 人力资源     |
8|    4 | yuanhao   | 销售         |
9|    5 | liwenzhou | 技术         |
10| NULL | NULL      | 运营         |
11+------+-----------+--------------+

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5 全外连接：显示左右两个表全部记录

1全外连接：在内连接的基础上增加左边有右边没有的和右边有左边没有的结果
2#注意：mysql不支持全外连接 full JOIN
3#强调：mysql可以使用此种方式间接实现全外连接

1select * from employee left join department on employee.dep_id = department.id
2union
3select * from employee right join department on employee.dep_id = department.id
4;
5#查看结果
6+------+------------+--------+------+--------+------+--------------+
7| id   | name       | sex    | age  | dep_id | id   | name         |
8+------+------------+--------+------+--------+------+--------------+
9|    1 | egon       | male   |   18 |    200 |  200 | 技术         |
10|    5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
11|    2 | alex       | female |   48 |    201 |  201 | 人力资源     |
12|    3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
13|    4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
14|    6 | jingliyang | female |   18 |    204 | NULL | NULL         |
15| NULL | NULL       | NULL   | NULL |   NULL |  203 | 运营         |
16+------+------------+--------+------+--------+------+--------------+
17
18#注意 union与union all的区别：union会去掉相同的纪录

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三符合条件连接查询

1#示例1：以内连接的方式查询employee和department表，并且employee表中的age字段值必须大于25,即找出年龄大于25岁的员工以及员工所在的部门
2select employee.name,department.name from employee inner join department
3    on employee.dep_id = department.id
4    where age > 25;
5
6#示例2：以内连接的方式查询employee和department表，并且以age字段的升序方式显示
7select employee.id,employee.name,employee.age,department.name from employee,department
8    where employee.dep_id = department.id
9    and age > 25
10    order by age asc;

四、子查询：

1#1：子查询是将一个查询语句嵌套在另一个查询语句中。
2#2：内层查询语句的查询结果，可以为外层查询语句提供查询条件。
3#3：子查询中可以包含：IN、NOT IN、ANY、ALL、EXISTS 和 NOT EXISTS等关键字
4#4：还可以包含比较运算符：= 、 !=、> 、<等

1、带 in 关键字的字查询

1查询平均年龄在25岁以上的部门名
2select id,name from department
3    where id in 
4        (select dep_id from employee group by dep_id having avg(age) > 25);
5
6#查看技术部员工姓名
7select name from employee
8    where dep_id in 
9        (select id from department where name='技术');
10
11#查看不足1人的部门名(子查询得到的是有人的部门id)
12select name from department where id not in (select distinct dep_id from employee);

2、带比较运算符的子查询

1#比较运算符：=、!=、>、>=、<、<=、<>
2#查询大于所有人平均年龄的员工名与年龄
3mysql> select name,age from emp where age > (select avg(age) from emp);
4+---------+------+
5| name | age |
6+---------+------+
7| alex | 48 |
8| wupeiqi | 38 |
9+---------+------+
102 rows in set (0.00 sec)
11
12
13#查询大于部门内平均年龄的员工名、年龄
14select t1.name,t1.age from emp t1
15inner join 
16(select dep_id,avg(age) avg_age from emp group by dep_id) t2
17on t1.dep_id = t2.dep_id
18where t1.age > t2.avg_age;

3 带EXISTS关键字的子查询

**EXISTS关字键字表示存在。**在使用EXISTS关键字时，内层查询语句不返回查询的记录。
而是返回一个真假值。True或False
当返回True时，外层查询语句将进行查询；当返回值为False时，外层查询语句不进行查询

1#department表中存在dept_id=203，Ture
2mysql> select * from employee
3    ->     where exists
4    ->         (select id from department where id=200);
5+----+------------+--------+------+--------+
6| id | name       | sex    | age  | dep_id |
7+----+------------+--------+------+--------+
8|  1 | egon       | male   |   18 |    200 |
9|  2 | alex       | female |   48 |    201 |
10|  3 | wupeiqi    | male   |   38 |    201 |
11|  4 | yuanhao    | female |   28 |    202 |
12|  5 | liwenzhou  | male   |   18 |    200 |
13|  6 | jingliyang | female |   18 |    204 |
14+----+------------+--------+------+--------+
15
16#department表中存在dept_id=205，False
17mysql> select * from employee
18    ->     where exists
19    ->         (select id from department where id=204);
20Empty set (0.00 sec)

练习：查询每个部分新入职的那位员工

准备表：

1company.employee
2    员工id      id                  int             
3    姓名        emp_name            varchar
4    性别        sex                 enum
5    年龄        age                 int
6    入职日期     hire_date           date
7    岗位        post                varchar
8    职位描述     post_comment        varchar
9    薪水        salary              double
10    办公室       office              int
11    部门编号     depart_id           int
12
13
14
15#创建表
16create table employee(
17id int not null unique auto_increment,
18name varchar(20) not null,
19sex enum('male','female') not null default 'male', #大部分是男的
20age int(3) unsigned not null default 28,
21hire_date date not null,
22post varchar(50),
23post_comment varchar(100),
24salary double(15,2),
25office int, #一个部门一个屋子
26depart_id int
27);
28
29
30#查看表结构
31mysql> desc employee;
32+--------------+-----------------------+------+-----+---------+----------------+
33| Field        | Type                  | Null | Key | Default | Extra          |
34+--------------+-----------------------+------+-----+---------+----------------+
35| id           | int(11)               | NO   | PRI | NULL    | auto_increment |
36| name         | varchar(20)           | NO   |     | NULL    |                |
37| sex          | enum('male','female') | NO   |     | male    |                |
38| age          | int(3) unsigned       | NO   |     | 28      |                |
39| hire_date    | date                  | NO   |     | NULL    |                |
40| post         | varchar(50)           | YES  |     | NULL    |                |
41| post_comment | varchar(100)          | YES  |     | NULL    |                |
42| salary       | double(15,2)          | YES  |     | NULL    |                |
43| office       | int(11)               | YES  |     | NULL    |                |
44| depart_id    | int(11)               | YES  |     | NULL    |                |
45+--------------+-----------------------+------+-----+---------+----------------+
46
47#插入记录
48#三个部门：教学，销售，运营
49insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
50('egon','male',18,'20170301','老男孩驻沙河办事处外交大使',7300.33,401,1), #以下是教学部
51('alex','male',78,'20150302','teacher',1000000.31,401,1),
52('wupeiqi','male',81,'20130305','teacher',8300,401,1),
53('yuanhao','male',73,'20140701','teacher',3500,401,1),
54('liwenzhou','male',28,'20121101','teacher',2100,401,1),
55('jingliyang','female',18,'20110211','teacher',9000,401,1),
56('jinxin','male',18,'19000301','teacher',30000,401,1),
57('成龙','male',48,'20101111','teacher',10000,401,1),
58
59('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
60('丫丫','female',38,'20101101','sale',2000.35,402,2),
61('丁丁','female',18,'20110312','sale',1000.37,402,2),
62('星星','female',18,'20160513','sale',3000.29,402,2),
63('格格','female',28,'20170127','sale',4000.33,402,2),
64
65('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
66('程咬金','male',18,'19970312','operation',20000,403,3),
67('程咬银','female',18,'20130311','operation',19000,403,3),
68('程咬铜','male',18,'20150411','operation',18000,403,3),
69('程咬铁','female',18,'20140512','operation',17000,403,3)
70;
71
72#ps：如果在windows系统中，插入中文字符，select的结果为空白，可以将所有字符编码统一设置成gbk
73
74准备表和记录

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答案：

1SELECT
2    *
3FROM
4    employee AS t1
5INNER JOIN (
6    SELECT
7        post,
8        max(hire_date) max_date
9    FROM
10        employee
11    GROUP BY
12        post
13) AS t2 ON t1.post = t2.post
14WHERE
15    t1.hire_date = t2.max_date;

五、综合练习

http://www.cnblogs.com/linhaifeng/articles/7895711.html#\_label2

先建立库 create database db7;

在切换到库 use db7;

粘贴数据：

ini.sql文件内容：

1/*
2 数据导入：
3 Navicat Premium Data Transfer
4
5 Source Server         : localhost
6 Source Server Type    : MySQL
7 Source Server Version : 50624
8 Source Host           : localhost
9 Source Database       : sqlexam
10
11 Target Server Type    : MySQL
12 Target Server Version : 50624
13 File Encoding         : utf-8
14
15 Date: 10/21/2016 06:46:46 AM
16*/
17
18SET NAMES utf8;
19SET FOREIGN_KEY_CHECKS = 0;
20
21-- ----------------------------
22--  Table structure for `class`
23-- ----------------------------
24DROP TABLE IF EXISTS `class`;
25CREATE TABLE `class` (
26  `cid` int(11) NOT NULL AUTO_INCREMENT,
27  `caption` varchar(32) NOT NULL,
28  PRIMARY KEY (`cid`)
29) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
30
31-- ----------------------------
32--  Records of `class`
33-- ----------------------------
34BEGIN;
35INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
36COMMIT;
37
38-- ----------------------------
39--  Table structure for `course`
40-- ----------------------------
41DROP TABLE IF EXISTS `course`;
42CREATE TABLE `course` (
43  `cid` int(11) NOT NULL AUTO_INCREMENT,
44  `cname` varchar(32) NOT NULL,
45  `teacher_id` int(11) NOT NULL,
46  PRIMARY KEY (`cid`),
47  KEY `fk_course_teacher` (`teacher_id`),
48  CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
49) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
50
51-- ----------------------------
52--  Records of `course`
53-- ----------------------------
54BEGIN;
55INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
56COMMIT;
57
58-- ----------------------------
59--  Table structure for `score`
60-- ----------------------------
61DROP TABLE IF EXISTS `score`;
62CREATE TABLE `score` (
63  `sid` int(11) NOT NULL AUTO_INCREMENT,
64  `student_id` int(11) NOT NULL,
65  `course_id` int(11) NOT NULL,
66  `num` int(11) NOT NULL,
67  PRIMARY KEY (`sid`),
68  KEY `fk_score_student` (`student_id`),
69  KEY `fk_score_course` (`course_id`),
70  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
71  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
72) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;
73
74-- ----------------------------
75--  Records of `score`
76-- ----------------------------
77BEGIN;
78INSERT 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');
79COMMIT;
80
81-- ----------------------------
82--  Table structure for `student`
83-- ----------------------------
84DROP TABLE IF EXISTS `student`;
85CREATE TABLE `student` (
86  `sid` int(11) NOT NULL AUTO_INCREMENT,
87  `gender` char(1) NOT NULL,
88  `class_id` int(11) NOT NULL,
89  `sname` varchar(32) NOT NULL,
90  PRIMARY KEY (`sid`),
91  KEY `fk_class` (`class_id`),
92  CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
93) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;
94
95-- ----------------------------
96--  Records of `student`
97-- ----------------------------
98BEGIN;
99INSERT 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');
100COMMIT;
101
102-- ----------------------------
103--  Table structure for `teacher`
104-- ----------------------------
105DROP TABLE IF EXISTS `teacher`;
106CREATE TABLE `teacher` (
107  `tid` int(11) NOT NULL AUTO_INCREMENT,
108  `tname` varchar(32) NOT NULL,
109  PRIMARY KEY (`tid`)
110) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
111
112-- ----------------------------
113--  Records of `teacher`
114-- ----------------------------
115BEGIN;
116INSERT 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');
117COMMIT;
118
119SET FOREIGN_KEY_CHECKS = 1;

View Code

题目及答案：

11、查询所有的课程的名称以及对应的任课老师姓名
2
32、查询学生表中男女生各有多少人
4
53、查询物理成绩等于100的学生的姓名
6
74、查询平均成绩大于八十分的同学的姓名和平均成绩
8
9SELECT
10    student.sname,
11    t1.avg_num
12FROM
13    student
14INNER JOIN (                      inner join # 内连接
15    SELECT
16        student_id,
17        avg(num) AS avg_num
18    FROM
19        score
20    GROUP BY
21        student_id
22    HAVING
23        avg(num) > 80
24) AS t1 ON student.sid = t1.student_id;
25
26
27
285、查询所有学生的学号，姓名，选课数，总成绩
29
30外链接之左连接：优先显示左表全部记录
31#本质就是：在内连接的基础上增加左边有右边没有的结果
32SELECT
33    student.sid,
34    student.sname,
35    t1.course_num,
36    t1.total_num
37FROM
38    student
39LEFT JOIN (
40    SELECT
41        student_id,
42        COUNT(course_id) course_num,
43        sum(num) total_num
44    FROM
45        score
46    GROUP BY
47        student_id
48) AS t1 ON student.sid = t1.student_id;
49
506、 查询姓李老师的个数
51
52select count(tid) 姓李人数 from teacher where tname like '李%';
53
547、 查询没有报李平老师课的学生姓名

1SELECT
2    student.sname
3FROM
4    student
5WHERE
6    sid NOT IN (
7        SELECT DISTINCT
8            student_id
9        FROM
10            score
11        WHERE
12            course_id IN (
13                SELECT
14                    course.cid
15                FROM
16                    course
17                INNER JOIN teacher ON course.teacher_id = teacher.tid
18                WHERE
19                    teacher.tname = '李平老师'
20            )
21    );

View Code

8、 查询物理课程比生物课程高的学生的学号

1SELECT
2    t1.student_id
3FROM
4    (
5        SELECT
6            student_id,
7            num
8        FROM
9            score
10        WHERE
11            course_id = (
12                SELECT
13                    cid
14                FROM
15                    course
16                WHERE
17                    cname = '物理'
18            )
19    ) AS t1
20INNER JOIN (
21    SELECT
22        student_id,
23        num
24    FROM
25        score
26    WHERE
27        course_id = (
28            SELECT
29                cid
30            FROM
31                course
32            WHERE
33                cname = '生物'
34        )
35) AS t2 ON t1.student_id = t2.student_id
36WHERE
37    t1.num > t2.num;

View Code

19、 查询没有同时选修物理课程和体育课程的学生姓名
2
310、查询挂科超过两门(包括两门)的学生姓名和班级
4、查询选修了所有课程的学生姓名
5
612、查询李平老师教的课程的所有成绩记录
7 
813、查询全部学生都选修了的课程号和课程名
9
1014、查询每门课程被选修的次数
11
1215、查询之选修了一门课程的学生姓名和学号
13
1416、查询所有学生考出的成绩并按从高到低排序（成绩去重）
15
1617、查询平均成绩大于85的学生姓名和平均成绩
17
1818、查询生物成绩不及格的学生姓名和对应生物分数
19
2019、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
21
2220、查询每门课程成绩最好的前两名学生姓名
23
2421、查询不同课程但成绩相同的学号，课程号，成绩
25
2622、查询没学过“叶平”老师课程的学生姓名以及选修的课程名称；
27
2823、查询所有选修了学号为1的同学选修过的一门或者多门课程的同学学号和姓名；
29
3024、任课最多的老师中学生单科成绩最高的学生姓名

参考：https://www.cnblogs.com/linhaifeng/articles/7267596.html#\_label2

！！！重中之重：练习之前务必搞清楚sql逻辑查询语句的执行顺序

链接：http://www.cnblogs.com/linhaifeng/articles/7372774.html

参考答案:http://www.cnblogs.com/linhaifeng/articles/7895711.html

一、准备表

二、多表连接查询

三符合条件连接查询

四、子查询：

五、综合练习

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9 MySQL

一、准备表

二、多表连接查询

三 符合条件连接查询

四、子查询：

五、综合练习

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