（第十五集——第2章）MySQL数据操作
2024-05-29 10:57:39
数据操作介绍
在MySQL管理软件中，可以通过SQL语句中的DML语言来实现数据的操作，包括
使用INSERT实现数据的插入
UPDATE实现数据的更新
使用DELETE实现数据的删除
使用SELECT查询数据以及。
插入数据INSERT
1. 插入完整数据（顺序插入）语法一：INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n);语法二：INSERT INTO 表名 VALUES (值1,值2,值3…值n);2. 指定字段插入数据语法：INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…);3. 插入多条记录语法：INSERT INTO 表名 VALUES(值1,值2,值3…值n),(值1,值2,值3…值n),(值1,值2,值3…值n);4. 插入查询结果语法：INSERT INTO 表名(字段1,字段2,字段3…字段n) SELECT (字段1,字段2,字段3…字段n) FROM 表2WHERE …;更新数据UPDATE
语法：UPDATE 表名 SET字段1=值1,字段2=值2,WHERE CONDITION;示例：UPDATE mysql.user SET password=password(‘123’) where user=’root’ and host=’localhost’;删除数据DELETE
语法：DELETE FROM 表名 WHERE CONITION;示例：DELETE FROM mysql.user WHERE password=’’;单表查询
单表查询的语法
SELECT 字段1,字段2... FROM 表名WHERE 条件GROUP BY fieldHAVING 筛选ORDER BY fieldLIMIT 限制条数关键字的执行优先级(重点)
重点中的重点：关键字的执行优先级
from
where
group by
having
select
distinct
order by
limit简单查询
数据准备：
company.employee员工id id int 姓名 emp_name varchar性别 sex enum年龄 age int入职日期 hire_date date岗位 post varchar职位描述 post_comment varchar薪水 salary double办公室 office int部门编号 depart_id int#创建表
create table employee(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum('male','female') not null default 'male', #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一个部门一个屋子
depart_id int
);#查看表结构
mysql> desc employee;
+--------------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| sex | enum('male','female') | NO | | male | |
| age | int(3) unsigned | NO | | 28 | |
| hire_date | date | NO | | NULL | |
| post | varchar(50) | YES | | NULL | |
| post_comment | varchar(100) | YES | | NULL | |
| salary | double(15,2) | YES | | NULL | |
| office | int(11) | YES | | NULL | |
| depart_id | int(11) | YES | | NULL | |
+--------------+-----------------------+------+-----+---------+----------------+#插入记录
#三个部门：教学，销售，运营
insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
('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
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龙','male',48,'20101111','teacher',10000,401,1),('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('丫丫','female',38,'20101101','sale',2000.35,402,2),
('丁丁','female',18,'20110312','sale',1000.37,402,2),
('星星','female',18,'20160513','sale',3000.29,402,2),
('格格','female',28,'20170127','sale',4000.33,402,2),('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬银','female',18,'20130311','operation',19000,403,3),
('程咬铜','male',18,'20150411','operation',18000,403,3),
('程咬铁','female',18,'20140512','operation',17000,403,3)
;#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简单查询：
#简单查询SELECT id,name,sex,age,hire_date,post,post_comment,salary,office,depart_id FROM employee;SELECT * FROM employee;SELECT name,salary FROM employee;#避免重复DISTINCTSELECT DISTINCT post FROM employee; #通过四则运算查询SELECT name, salary*12 FROM employee;SELECT name, salary*12 AS Annual_salary FROM employee;SELECT name, salary*12 Annual_salary FROM employee;#定义显示格式CONCAT() 函数用于连接字符串SELECT CONCAT('姓名: ',name,' 年薪: ', salary*12) AS Annual_salary FROM employee;CONCAT_WS() 第一个参数为分隔符SELECT CONCAT_WS(':',name,salary*12) AS Annual_salary FROM employee;结合CASE语句：SELECT(CASEWHEN NAME = 'egon' THENNAMEWHEN NAME = 'alex' THENCONCAT(name,'_BIGSB')ELSEconcat(NAME, 'SB')END) as new_nameFROMemp;小练习：
1 查出所有员工的名字，薪资,格式为
<名字:egon> <薪资:3000>
2 查出所有的岗位（去掉重复）
3 查出所有员工名字，以及他们的年薪,年薪的字段名为annual_year
select concat('<名字:',name,'> ','<薪资:',salary,'>') from employee;
select distinct depart_id from employee;
select name,salary*12 annual_salary from employee;WHERE约束
where字句中可以使用：
1. 比较运算符：> < >= <= <> !=
2. between 80 and 100 值在10到20之间
3. in(80,90,100) 值是10或20或30
4. like 'egon%'pattern可以是%或_，%表示任意多字符_表示一个字符
5. 逻辑运算符：在多个条件直接可以使用逻辑运算符 and or not#1:单条件查询SELECT name FROM employeeWHERE post='sale';#2:多条件查询SELECT name,salary FROM employeeWHERE post='teacher' AND salary>10000;#3:关键字BETWEEN ANDSELECT name,salary FROM employee WHERE salary BETWEEN 10000 AND 20000;SELECT name,salary FROM employee WHERE salary NOT BETWEEN 10000 AND 20000;#4:关键字IS NULL(判断某个字段是否为NULL不能用等号，需要用IS)SELECT name,post_comment FROM employee WHERE post_comment IS NULL;SELECT name,post_comment FROM employee WHERE post_comment IS NOT NULL;SELECT name,post_comment FROM employee WHERE post_comment=''; 注意''是空字符串，不是nullps：执行update employee set post_comment='' where id=2;再用上条查看，就会有结果了#5:关键字IN集合查询SELECT name,salary FROM employee WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;SELECT name,salary FROM employee WHERE salary IN (3000,3500,4000,9000) ;SELECT name,salary FROM employee WHERE salary NOT IN (3000,3500,4000,9000) ;#6:关键字LIKE模糊查询通配符’%’SELECT * FROM employee WHERE name LIKE 'eg%';通配符’_’SELECT * FROM employee WHERE name LIKE 'al__';小练习：
- 查看岗位是teacher的员工姓名、年龄
- 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
- 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
- 查看岗位描述不为NULL的员工信息
- 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
- 查看岗位是teacher且薪资不是10000或9000或30000的员工姓名、年龄、薪资
- 查看岗位是teacher且名字是jin开头的员工姓名、年薪
select name,age from employee where post = 'teacher';
select name,age from employee where post='teacher' and age > 30;
select name,age,salary from employee where post='teacher' and salary between 9000 and 10000;
select * from employee where post_comment is not null;
select name,age,salary from employee where post='teacher' and salary in (10000,9000,30000);
select name,age,salary from employee where post='teacher' and salary not in (10000,9000,30000);
select name,salary*12 from employee where post='teacher' and name like 'jin%';分组查询:GROUP BY
#1、首先明确一点：分组发生在where之后，即分组是基于where之后得到的记录而进行的#2、分组指的是：将所有记录按照某个相同字段进行归类，比如针对员工信息表的职位分组，或者按照性别进行分组等#3、为何要分组呢？取每个部门的最高工资取每个部门的员工数取男人数和女人数小窍门：‘每’这个字后面的字段，就是我们分组的依据#4、大前提：可以按照任意字段分组，但是分组完毕后，比如group by post，只能查看post字段，如果想查看组内信息，需要借助于聚合函数ONLY_FULL_GROUP_BY
#查看MySQL 5.7默认的sql_mode如下：
mysql> select @@global.sql_mode;
ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION#！！！注意
ONLY_FULL_GROUP_BY的语义就是确定select target list中的所有列的值都是明确语义，简单的说来，在ONLY_FULL_GROUP_BY模式下，target list中的值要么是来自于聚集函数的结果，要么是来自于group by list中的表达式的值。#设置sql_mole如下操作(我们可以去掉ONLY_FULL_GROUP_BY模式)：
mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';mysql> select @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
| |
+-------------------+
1 row in set (0.00 sec)mysql> select * from emp group by post;
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外交大使 | NULL | 7300.33 | 401 | 1 |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
4 rows in set (0.00 sec)#由于没有设置ONLY_FULL_GROUP_BY,于是也可以有结果，默认都是组内的第一条记录，但其实这是没有意义的mysql> set global sql_mode='ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)mysql> quit #设置成功后，一定要退出，然后重新登录方可生效
Byemysql> use db1;
Database changed
mysql> select * from emp group by post; #报错
ERROR 1055 (42000): 'db1.emp.id' isn't in GROUP BY
mysql> select post,count(id) from emp group by post; #只能查看分组依据和使用聚合函数
+----------------------------+-----------+
| post | count(id) |
+----------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+----------------------------+-----------+
4 rows in set (0.00 sec)GROUP BY
单独使用GROUP BY关键字分组SELECT post FROM employee GROUP BY post;注意：我们按照post字段分组，那么select查询的字段只能是post，想要获取组内的其他相关信息，需要借助函数GROUP BY关键字和GROUP_CONCAT()函数一起使用SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post;#按照岗位分组，并查看组内成员名SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post;GROUP BY与聚合函数一起使用select post,count(id) as count from employee group by post;#按照岗位分组，并查看每个组有多少人强调：
如果我们用unique的字段作为分组的依据，则每一条记录自成一组，这种分组没有意义，多条记录之间的某个字段值相同，该字段通常用来作为分组的依据。
聚合函数
#强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组示例：SELECT COUNT(*) FROM employee;SELECT COUNT(*) FROM employee WHERE depart_id=1;SELECT MAX(salary) FROM employee;SELECT MIN(salary) FROM employee;SELECT AVG(salary) FROM employee;SELECT SUM(salary) FROM employee;SELECT SUM(salary) FROM employee WHERE depart_id=3;小练习：
- 查询岗位名以及岗位包含的所有员工名字
- 查询岗位名以及各岗位内包含的员工个数
- 查询公司内男员工和女员工的个数
- 查询岗位名以及各岗位的平均薪资
- 查询岗位名以及各岗位的最高薪资
- 查询岗位名以及各岗位的最低薪资
- 查询男员工与男员工的平均薪资，女员工与女员工的平均薪资
#题1：分组
mysql> select post,group_concat(name) from employee group by post;
+-----------------------------------------+---------------------------------------------------------+
| post | group_concat(name) |
+-----------------------------------------+---------------------------------------------------------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| sale | 歪歪,丫丫,丁丁,星星,格格 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
| 老男孩驻沙河办事处外交大使 | egon |
+-----------------------------------------+---------------------------------------------------------+#题目2：
mysql> select post,count(id) from employee group by post;
+-----------------------------------------+-----------+
| post | count(id) |
+-----------------------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+-----------------------------------------+-----------+#题目3：
mysql> select sex,count(id) from employee group by sex;
+--------+-----------+
| sex | count(id) |
+--------+-----------+
| male | 10 |
| female | 8 |
+--------+-----------+#题目4：
mysql> select post,avg(salary) from employee group by post;
+-----------------------------------------+---------------+
| post | avg(salary) |
+-----------------------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 老男孩驻沙河办事处外交大使 | 7300.330000 |
+-----------------------------------------+---------------+#题目5
mysql> select post,max(salary) from employee group by post;
+-----------------------------------------+-------------+
| post | max(salary) |
+-----------------------------------------+-------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 老男孩驻沙河办事处外交大使 | 7300.33 |
+-----------------------------------------+-------------+#题目6
mysql> select post,min(salary) from employee group by post;
+-----------------------------------------+-------------+
| post | min(salary) |
+-----------------------------------------+-------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 老男孩驻沙河办事处外交大使 | 7300.33 |
+-----------------------------------------+-------------+#题目七
mysql> select sex,avg(salary) from employee group by sex;
+--------+---------------+
| sex | avg(salary) |
+--------+---------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+---------------+HAVING过滤
HAVING与WHERE不一样的地方在于!!!!!!
#！！！执行优先级从高到低：where > group by > having
#1. Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。
#2. Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数mysql> select @@sql_mode;
+--------------------+
| @@sql_mode |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
1 row in set (0.00 sec)mysql> select * from emp where salary > 100000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec)mysql> select * from emp having salary > 100000;
ERROR 1463 (42000): Non-grouping field 'salary' is used in HAVING clausemysql> select post,group_concat(name) from emp group by post having salary > 10000;#错误，分组后无法直接取到salary字段
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
mysql> select post,group_concat(name) from emp group by post having avg(salary) > 10000;
+-----------+-------------------------------------------------------+
| post | group_concat(name) |
+-----------+-------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
+-----------+-------------------------------------------------------+
2 rows in set (0.00 sec)小练习
- 查询各岗位内包含的员工个数小于2的岗位名、岗位内包含员工名字、个数
- 查询各岗位平均薪资大于10000的岗位名、平均工资
- 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资
#题1：
mysql> select post,group_concat(name),count(id) from employee group by post having count(id) < 2;
+-----------------------------------------+--------------------+-----------+
| post | group_concat(name) | count(id) |
+-----------------------------------------+--------------------+-----------+
| 老男孩驻沙河办事处外交大使 | egon | 1 |
+-----------------------------------------+--------------------+-----------+#题目2：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+#题目3：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) <20000;
+-----------+--------------+
| post | avg(salary) |
+-----------+--------------+
| operation | 16800.026000 |
+-----------+--------------+查询排序:ORDER BY
按单列排序SELECT * FROM employee ORDER BY salary;SELECT * FROM employee ORDER BY salary ASC;SELECT * FROM employee ORDER BY salary DESC;按多列排序:先按照age排序，如果年纪相同，则按照薪资排序SELECT * from employeeORDER BY age,salary DESC;小练习：
- 查询所有员工信息，先按照age升序排序，如果age相同则按照hire_date降序排序
- 查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资升序排列
- 查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资降序排列
#题目1
mysql> select * from employee ORDER BY age asc,hire_date desc;#题目2
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+#题目3
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| teacher | 151842.901429 |
| operation | 16800.026000 |
+-----------+---------------+限制查询的记录数:LIMIT
示例：SELECT * FROM employee ORDER BY salary DESC LIMIT 3; #默认初始位置为0 SELECT * FROM employee ORDER BY salary DESCLIMIT 0,5; #从第0开始，即先查询出第一条，然后包含这一条在内往后查5条SELECT * FROM employee ORDER BY salary DESCLIMIT 5,5; #从第5开始，即先查询出第6条，然后包含这一条在内往后查5条使用正则表达式查询
SELECT * FROM employee WHERE name REGEXP '^ale';SELECT * FROM employee WHERE name REGEXP 'on$';SELECT * FROM employee WHERE name REGEXP 'm{2}';小结：对字符串匹配的方式
WHERE name = 'egon';
WHERE name LIKE 'yua%';
WHERE name REGEXP 'on$';小练习：
查看所有员工中名字是jin开头，n或者g结尾巴的员工信息
select * from employee where name regexp '^jin.*[gn]$';多表查询
准备表
#建表
create table department(
id int,
name varchar(20)
);create table employee(
id int primary key auto_increment,
name varchar(20),
sex enum('male','female') not null default 'male',
age int,
dep_id int
);#插入数据
insert into department values
(200,'技术'),
(201,'人力资源'),
(202,'销售'),
(203,'运营');insert into employee(name,sex,age,dep_id) values
('egon','male',18,200),
('alex','female',48,201),
('wupeiqi','male',38,201),
('yuanhao','female',28,202),
('liwenzhou','male',18,200),
('jingliyang','female',18,204)
;
#查看表结构和数据
mysql> desc department;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+mysql> desc employee;
+--------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | YES | | NULL | |
| sex | enum('male','female') | NO | | male | |
| age | int(11) | YES | | NULL | |
| dep_id | int(11) | YES | | NULL | |
+--------+-----------------------+------+-----+---------+----------------+mysql> select * from department;
+------+--------------+
| id | name |
+------+--------------+
| 200 | 技术 |
| 201 | 人力资源 |
| 202 | 销售 |
| 203 | 运营 |
+------+--------------+mysql> select * from employee;
+----+------------+--------+------+--------+
| id | name | sex | age | dep_id |
+----+------------+--------+------+--------+
| 1 | egon | male | 18 | 200 |
| 2 | alex | female | 48 | 201 |
| 3 | wupeiqi | male | 38 | 201 |
| 4 | yuanhao | female | 28 | 202 |
| 5 | liwenzhou | male | 18 | 200 |
| 6 | jingliyang | female | 18 | 204 |
+----+------------+--------+------+--------+多表连接查询
#重点：外链接语法SELECT 字段列表FROM 表1 INNER|LEFT|RIGHT JOIN 表2ON 表1.字段 = 表2.字段;交叉连接：不适用任何匹配条件。生成笛卡尔积
mysql> select * from employee,department;
+----+------------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+----+------------+--------+------+--------+------+--------------+
| 1 | egon | male | 18 | 200 | 200 | 技术 |
| 1 | egon | male | 18 | 200 | 201 | 人力资源 |
| 1 | egon | male | 18 | 200 | 202 | 销售 |
| 1 | egon | male | 18 | 200 | 203 | 运营 |
| 2 | alex | female | 48 | 201 | 200 | 技术 |
| 2 | alex | female | 48 | 201 | 201 | 人力资源 |
| 2 | alex | female | 48 | 201 | 202 | 销售 |
| 2 | alex | female | 48 | 201 | 203 | 运营 |
| 3 | wupeiqi | male | 38 | 201 | 200 | 技术 |
| 3 | wupeiqi | male | 38 | 201 | 201 | 人力资源 |
| 3 | wupeiqi | male | 38 | 201 | 202 | 销售 |
| 3 | wupeiqi | male | 38 | 201 | 203 | 运营 |
| 4 | yuanhao | female | 28 | 202 | 200 | 技术 |
| 4 | yuanhao | female | 28 | 202 | 201 | 人力资源 |
| 4 | yuanhao | female | 28 | 202 | 202 | 销售 |
| 4 | yuanhao | female | 28 | 202 | 203 | 运营 |
| 5 | liwenzhou | male | 18 | 200 | 200 | 技术 |
| 5 | liwenzhou | male | 18 | 200 | 201 | 人力资源 |
| 5 | liwenzhou | male | 18 | 200 | 202 | 销售 |
| 5 | liwenzhou | male | 18 | 200 | 203 | 运营 |
| 6 | jingliyang | female | 18 | 204 | 200 | 技术 |
| 6 | jingliyang | female | 18 | 204 | 201 | 人力资源 |
| 6 | jingliyang | female | 18 | 204 | 202 | 销售 |
| 6 | jingliyang | female | 18 | 204 | 203 | 运营 |
+----+------------+--------+------+--------+------+--------------+内连接：只连接匹配的行
#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
#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
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee inner join department on employee.dep_id=department.id;
+----+-----------+------+--------+--------------+
| id | name | age | sex | name |
+----+-----------+------+--------+--------------+
| 1 | egon | 18 | male | 技术 |
| 2 | alex | 48 | female | 人力资源 |
| 3 | wupeiqi | 38 | male | 人力资源 |
| 4 | yuanhao | 28 | female | 销售 |
| 5 | liwenzhou | 18 | male | 技术 |
+----+-----------+------+--------+--------------+#上述sql等同于
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id=department.id;外链接之左连接：优先显示左表全部记录
#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
#本质就是：在内连接的基础上增加左边有右边没有的结果
mysql> select employee.id,employee.name,department.name as depart_name from employee left join department on employee.dep_id=department.id;
+----+------------+--------------+
| id | name | depart_name |
+----+------------+--------------+
| 1 | egon | 技术 |
| 5 | liwenzhou | 技术 |
| 2 | alex | 人力资源 |
| 3 | wupeiqi | 人力资源 |
| 4 | yuanhao | 销售 |
| 6 | jingliyang | NULL |
+----+------------+--------------+外链接之右连接：优先显示右表全部记录
#以右表为准，即找出所有部门信息，包括没有员工的部门
#本质就是：在内连接的基础上增加右边有左边没有的结果
mysql> select employee.id,employee.name,department.name as depart_name from employee right join department on employee.dep_id=department.id;
+------+-----------+--------------+
| id | name | depart_name |
+------+-----------+--------------+
| 1 | egon | 技术 |
| 2 | alex | 人力资源 |
| 3 | wupeiqi | 人力资源 |
| 4 | yuanhao | 销售 |
| 5 | liwenzhou | 技术 |
| NULL | NULL | 运营 |
+------+-----------+--------------+全外连接：显示左右两个表全部记录
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
#注意：mysql不支持全外连接 full JOIN
#强调：mysql可以使用此种方式间接实现全外连接
select * from employee left join department on employee.dep_id = department.id
union
select * from employee right join department on employee.dep_id = department.id
;
#查看结果
+------+------------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+------+------------+--------+------+--------+------+--------------+
| 1 | egon | male | 18 | 200 | 200 | 技术 |
| 5 | liwenzhou | male | 18 | 200 | 200 | 技术 |
| 2 | alex | female | 48 | 201 | 201 | 人力资源 |
| 3 | wupeiqi | male | 38 | 201 | 201 | 人力资源 |
| 4 | yuanhao | female | 28 | 202 | 202 | 销售 |
| 6 | jingliyang | female | 18 | 204 | NULL | NULL |
| NULL | NULL | NULL | NULL | NULL | 203 | 运营 |
+------+------------+--------+------+--------+------+--------------+#注意 union与union all的区别：union会去掉相同的纪录符合条件连接查询
#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
select employee.name,department.name from employee inner join departmenton employee.dep_id = department.idwhere age > 25;#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
select employee.id,employee.name,employee.age,department.name from employee,departmentwhere employee.dep_id = department.idand age > 25order by age asc;子查询
#1：子查询是将一个查询语句嵌套在另一个查询语句中。
#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：子查询中可以包含：IN、NOT IN、ANY、ALL、EXISTS 和 NOT EXISTS等关键字
#4：还可以包含比较运算符：= 、 !=、> 、<等带IN关键字的子查询
#查询平均年龄在25岁以上的部门名
select id,name from departmentwhere id in (select dep_id from employee group by dep_id having avg(age) > 25);#查看技术部员工姓名
select name from employeewhere dep_id in (select id from department where name='技术');#查看不足1人的部门名(子查询得到的是有人的部门id)
select name from department where id not in (select distinct dep_id from employee);带比较运算符的子查询
#比较运算符：=、!=、>、>=、<、<=、<>
#查询大于所有人平均年龄的员工名与年龄
mysql> select name,age from emp where age > (select avg(age) from emp);
+---------+------+
| name | age |
+---------+------+
| alex | 48 |
| wupeiqi | 38 |
+---------+------+
2 rows in set (0.00 sec)#查询员工中大于部门内平均年龄的员工名、年龄
select t1.name,t1.age from emp as t1
inner join
(select dep_id,avg(age) as avg_age from emp group by dep_id) as t2
on t1.dep_id = t2.dep_id
where t1.age > t2.avg_age; 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。
#department表中存在dept_id=203，Ture
mysql> select * from employee-> where exists-> (select id from department where id=200);
+----+------------+--------+------+--------+
| id | name | sex | age | dep_id |
+----+------------+--------+------+--------+
| 1 | egon | male | 18 | 200 |
| 2 | alex | female | 48 | 201 |
| 3 | wupeiqi | male | 38 | 201 |
| 4 | yuanhao | female | 28 | 202 |
| 5 | liwenzhou | male | 18 | 200 |
| 6 | jingliyang | female | 18 | 204 |
+----+------------+--------+------+--------+#department表中存在dept_id=205，False
mysql> select * from employee-> where exists-> (select id from department where id=204);
Empty set (0.00 sec)查询每个部门最新入职的那位员工
company.employee员工id id int 姓名 emp_name varchar性别 sex enum年龄 age int入职日期 hire_date date岗位 post varchar职位描述 post_comment varchar薪水 salary double办公室 office int部门编号 depart_id int#创建表
create table employee(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum('male','female') not null default 'male', #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一个部门一个屋子
depart_id int
);#查看表结构
mysql> desc employee;
+--------------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| sex | enum('male','female') | NO | | male | |
| age | int(3) unsigned | NO | | 28 | |
| hire_date | date | NO | | NULL | |
| post | varchar(50) | YES | | NULL | |
| post_comment | varchar(100) | YES | | NULL | |
| salary | double(15,2) | YES | | NULL | |
| office | int(11) | YES | | NULL | |
| depart_id | int(11) | YES | | NULL | |
+--------------+-----------------------+------+-----+---------+----------------+#插入记录
#三个部门：教学，销售，运营
insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
('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
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龙','male',48,'20101111','teacher',10000,401,1),('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('丫丫','female',38,'20101101','sale',2000.35,402,2),
('丁丁','female',18,'20110312','sale',1000.37,402,2),
('星星','female',18,'20160513','sale',3000.29,402,2),
('格格','female',28,'20170127','sale',4000.33,402,2),('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬银','female',18,'20130311','operation',19000,403,3),
('程咬铜','male',18,'20150411','operation',18000,403,3),
('程咬铁','female',18,'20140512','operation',17000,403,3)
;#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查询每个部门最新入职的那位员工 答案一：
SELECT*
FROMemp AS t1
INNER JOIN (SELECTpost,max(hire_date) max_dateFROMempGROUP BYpost
) AS t2 ON t1.post = t2.post
WHEREt1.hire_date = t2.max_date;SQL逻辑查询语句执行顺序： SELECT语句关键字的定义顺序
SELECT DISTINCT <select_list>
FROM <left_table>
<join_type> JOIN <right_table>
ON <join_condition>
WHERE <where_condition>
GROUP BY <group_by_list>
HAVING <having_condition>
ORDER BY <order_by_condition>
LIMIT <limit_number>SELECT语句关键字的执行顺序
(7) SELECT
(8) DISTINCT <select_list>
(1) FROM <left_table>
(3) <join_type> JOIN <right_table>
(2) ON <join_condition>
(4) WHERE <where_condition>
(5) GROUP BY <group_by_list>
(6) HAVING <having_condition>
(9) ORDER BY <order_by_condition>
(10) LIMIT <limit_number>准备表和数据
. 新建一个测试数据库TestDB；
create database TestDB;- 创建测试表table1和table2；
CREATE TABLE table1(customer_id VARCHAR(10) NOT NULL,city VARCHAR(10) NOT NULL,PRIMARY KEY(customer_id))ENGINE=INNODB DEFAULT CHARSET=UTF8;CREATE TABLE table2(order_id INT NOT NULL auto_increment,customer_id VARCHAR(10),PRIMARY KEY(order_id))ENGINE=INNODB DEFAULT CHARSET=UTF8;- 插入测试数据；
INSERT INTO table1(customer_id,city) VALUES('163','hangzhou');INSERT INTO table1(customer_id,city) VALUES('9you','shanghai');INSERT INTO table1(customer_id,city) VALUES('tx','hangzhou');INSERT INTO table1(customer_id,city) VALUES('baidu','hangzhou');INSERT INTO table2(customer_id) VALUES('163');INSERT INTO table2(customer_id) VALUES('163');INSERT INTO table2(customer_id) VALUES('9you');INSERT INTO table2(customer_id) VALUES('9you');INSERT INTO table2(customer_id) VALUES('9you');INSERT INTO table2(customer_id) VALUES('tx');INSERT INTO table2(customer_id) VALUES(NULL);- 准备工作做完以后，table1和table2看起来应该像下面这样：
mysql> select * from table1;+-------------+----------+| customer_id | city |+-------------+----------+| 163 | hangzhou || 9you | shanghai || baidu | hangzhou || tx | hangzhou |+-------------+----------+4 rows in set (0.00 sec)mysql> select * from table2;+----------+-------------+| order_id | customer_id |+----------+-------------+| 1 | 163 || 2 | 163 || 3 | 9you || 4 | 9you || 5 | 9you || 6 | tx || 7 | NULL |+----------+-------------+7 rows in set (0.00 sec)- 准备SQL逻辑查询测试语句
#查询来自杭州，并且订单数少于2的客户。SELECT a.customer_id, COUNT(b.order_id) as total_ordersFROM table1 AS aLEFT JOIN table2 AS bON a.customer_id = b.customer_idWHERE a.city = 'hangzhou'GROUP BY a.customer_idHAVING count(b.order_id) < 2ORDER BY total_orders DESC;执行顺序分析
在这些SQL语句的执行过程中，都会产生一个虚拟表，用来保存SQL语句的执行结果（这是重点），我现在就来跟踪这个虚拟表的变化，得到最终的查询结果的过程，来分析整个SQL逻辑查询的执行顺序和过程。
- 执行FROM语句
第一步，执行FROM语句。我们首先需要知道最开始从哪个表开始的，这就是FROM告诉我们的。现在有了和两个表，我们到底从哪个表开始，还是从两个表进行某种联系以后再开始呢？它们之间如何产生联系呢？——笛卡尔积
关于什么是笛卡尔积，请自行Google补脑。经过FROM语句对两个表执行笛卡尔积，会得到一个虚拟表，暂且叫VT1（vitual table 1），内容如下：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| 9you | shanghai | 1 | 163 |
| baidu | hangzhou | 1 | 163 |
| tx | hangzhou | 1 | 163 |
| 163 | hangzhou | 2 | 163 |
| 9you | shanghai | 2 | 163 |
| baidu | hangzhou | 2 | 163 |
| tx | hangzhou | 2 | 163 |
| 163 | hangzhou | 3 | 9you |
| 9you | shanghai | 3 | 9you |
| baidu | hangzhou | 3 | 9you |
| tx | hangzhou | 3 | 9you |
| 163 | hangzhou | 4 | 9you |
| 9you | shanghai | 4 | 9you |
| baidu | hangzhou | 4 | 9you |
| tx | hangzhou | 4 | 9you |
| 163 | hangzhou | 5 | 9you |
| 9you | shanghai | 5 | 9you |
| baidu | hangzhou | 5 | 9you |
| tx | hangzhou | 5 | 9you |
| 163 | hangzhou | 6 | tx |
| 9you | shanghai | 6 | tx |
| baidu | hangzhou | 6 | tx |
| tx | hangzhou | 6 | tx |
| 163 | hangzhou | 7 | NULL |
| 9you | shanghai | 7 | NULL |
| baidu | hangzhou | 7 | NULL |
| tx | hangzhou | 7 | NULL |
+-------------+----------+----------+-------------+总共有28（table1的记录条数 * table2的记录条数）条记录。这就是VT1的结果，接下来的操作就在VT1的基础上进行。
执行ON过滤
执行完笛卡尔积以后，接着就进行ON a.customer_id = b.customer_id条件过滤，根据ON中指定的条件，去掉那些不符合条件的数据，得到VT2表，内容如下：
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| 163 | hangzhou | 2 | 163 |
| 9you | shanghai | 3 | 9you |
| 9you | shanghai | 4 | 9you |
| 9you | shanghai | 5 | 9you |
| tx | hangzhou | 6 | tx |
+-------------+----------+----------+-------------+添加外部行
这一步只有在连接类型为OUTER JOIN时才发生，如LEFT OUTER JOIN、RIGHT OUTER JOIN和FULL OUTER JOIN。在大多数的时候，我们都是会省略掉OUTER关键字的，但OUTER表示的就是外部行的概念。
LEFT OUTER JOIN把左表记为保留表，得到的结果为：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| 163 | hangzhou | 2 | 163 |
| 9you | shanghai | 3 | 9you |
| 9you | shanghai | 4 | 9you |
| 9you | shanghai | 5 | 9you |
| tx | hangzhou | 6 | tx |
| baidu | hangzhou | NULL | NULL |
+-------------+----------+----------+-------------+RIGHT OUTER JOIN把右表记为保留表，得到的结果为：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| 163 | hangzhou | 2 | 163 |
| 9you | shanghai | 3 | 9you |
| 9you | shanghai | 4 | 9you |
| 9you | shanghai | 5 | 9you |
| tx | hangzhou | 6 | tx |
| NULL | NULL | 7 | NULL |
+-------------+----------+----------+-------------+FULL OUTER JOIN把左右表都作为保留表，得到的结果为：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| 163 | hangzhou | 2 | 163 |
| 9you | shanghai | 3 | 9you |
| 9you | shanghai | 4 | 9you |
| 9you | shanghai | 5 | 9you |
| tx | hangzhou | 6 | tx |
| baidu | hangzhou | NULL | NULL |
| NULL | NULL | 7 | NULL |
+-------------+----------+----------+-------------+添加外部行的工作就是在VT2表的基础上添加保留表中被过滤条件过滤掉的数据，非保留表中的数据被赋予NULL值，最后生成虚拟表VT3。
由于在准备的测试SQL查询逻辑语句中使用的是LEFT JOIN，过滤掉了以下这条数据：
| baidu | hangzhou | NULL | NULL |执行WHERE过滤
对添加外部行得到的VT3进行WHERE过滤，只有符合的记录才会输出到虚拟表VT4中。当我们执行WHERE a.city = ‘hangzhou’的时候，就会得到以下内容，并存在虚拟表VT4中：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| 163 | hangzhou | 2 | 163 |
| tx | hangzhou | 6 | tx |
| baidu | hangzhou | NULL | NULL |
+-------------+----------+----------+-------------+但是在使用WHERE子句时，需要注意以下两点：
由于数据还没有分组，因此现在还不能在WHERE过滤器中使用where_condition=MIN(col)这类对分组统计的过滤；
由于还没有进行列的选取操作，因此在SELECT中使用列的别名也是不被允许的，如：SELECT city as c FROM t WHERE c=’shanghai’;是不允许出现的。
执行GROUP BY分组
GROU BY子句主要是对使用WHERE子句得到的虚拟表进行分组操作。我们执行测试语句中的GROUP BY a.customer_id，就会得到以下内容(默认只显示组内第一条)：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| 163 | hangzhou | 1 | 163 |
| baidu | hangzhou | NULL | NULL |
| tx | hangzhou | 6 | tx |
+-------------+----------+----------+-------------+执行HAVING过滤
HAVING子句主要和GROUP BY子句配合使用，对分组得到的虚拟表进行条件过滤。当我执行测试语句中的HAVING count(b.order_id) < 2时，将得到以下内容：
+-------------+----------+----------+-------------+
| customer_id | city | order_id | customer_id |
+-------------+----------+----------+-------------+
| baidu | hangzhou | NULL | NULL |
| tx | hangzhou | 6 | tx |
+-------------+----------+----------+-------------+SELECT列表
现在才会执行到SELECT子句，不要以为SELECT子句被写在第一行，就是第一个被执行的。
我们执行测试语句中的SELECT a.customer_id, COUNT(b.order_id) as total_orders，从虚拟表VT6中选择出我们需要的内容。我们将得到以下内容：
+-------------+--------------+
| customer_id | total_orders |
+-------------+--------------+
| baidu | 0 |
| tx | 1 |
+-------------+--------------+执行DISTINCT子句
如果在查询中指定了DISTINCT子句，则会创建一张内存临时表（如果内存放不下，就需要存放在硬盘了）。这张临时表的表结构和上一步产生的虚拟表VT7是一样的，不同的是对进行DISTINCT操作的列增加了一个唯一索引，以此来除重复数据。
由于我的测试SQL语句中并没有使用DISTINCT，所以，在该查询中，这一步不会生成一个虚拟表。
执行ORDER BY子句
对虚拟表中的内容按照指定的列进行排序，然后返回一个新的虚拟表，我们执行测试SQL语句中的ORDER BY total_orders DESC，就会得到以下内容：
+-------------+--------------+
| customer_id | total_orders |
+-------------+--------------+
| tx | 1 |
| baidu | 0 |
+-------------+--------------+执行LIMIT子句
LIMIT子句从上一步得到的VT8虚拟表中选出从指定位置开始的指定行数据。对于没有应用ORDER BY的LIMIT子句，得到的结果同样是无序的，所以，很多时候，我们都会看到LIMIT子句会和ORDER BY子句一起使用。
MySQL数据库的LIMIT支持如下形式的选择：
LIMIT n, m表示从第n条记录开始选择m条记录。而很多开发人员喜欢使用该语句来解决分页问题。对于小数据，使用LIMIT子句没有任何问题，当数据量非常大的时候，使用LIMIT n, m是非常低效的。因为LIMIT的机制是每次都是从头开始扫描，如果需要从第60万行开始，读取3条数据，就需要先扫描定位到60万行，然后再进行读取，而扫描的过程是一个非常低效的过程。所以，对于大数据处理时，是非常有必要在应用层建立一定的缓存机制（现在的大数据处理，大都使用缓存）
.
综合练习
- 数据准备：
/*数据导入：Navicat Premium Data TransferSource Server : localhostSource Server Type : MySQLSource Server Version : 50624Source Host : localhostSource Database : sqlexamTarget Server Type : MySQLTarget Server Version : 50624File Encoding : utf-8Date: 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;
- 题目：
1、查询所有的课程的名称以及对应的任课老师姓名2、查询学生表中男女生各有多少人3、查询物理成绩等于100的学生的姓名4、查询平均成绩大于八十分的同学的姓名和平均成绩5、查询所有学生的学号，姓名，选课数，总成绩6、 查询姓李老师的个数7、 查询没有报李平老师课的学生姓名8、 查询物理课程比生物课程高的学生的学号9、 查询没有同时选修物理课程和体育课程的学生姓名10、查询挂科超过两门(包括两门)的学生姓名和班级11 、查询选修了所有课程的学生姓名12、查询李平老师教的课程的所有成绩记录13、查询全部学生都选修了的课程号和课程名14、查询每门课程被选修的次数15、查询之选修了一门课程的学生姓名和学号16、查询所有学生考出的成绩并按从高到低排序（成绩去重）17、查询平均成绩大于85的学生姓名和平均成绩18、查询生物成绩不及格的学生姓名和对应生物分数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20、查询每门课程成绩最好的前两名学生姓名21、查询不同课程但成绩相同的学号，课程号，成绩22、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；23、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；24、任课最多的老师中学生单科成绩最高的学生姓名答案：
# 查询所有的课程的名称以及对应的任课老师姓名
/*select course.cname, teacher.tname from course
inner join teacher on course.teacher_id = teacher_id;*/# 2、查询学生表中男女生各有多少人
# select gender as '性别', count(sid) as '人数' from student group by gender;#3、查询物理成绩等于100的学生的姓名
/*SELECT student.sname, t2.num, t2.cname
FROMstudentRIGHT JOIN(SELECT student_id, score.num, course.cnameFROMscoreinner JOIN course ON score.course_id = course.cidWHEREscore.num = 100AND course.cname = '物理') AS t2 ON student.sid = t2.student_id;*/# 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, t1.avg_num
FROMstudentINNER JOIN(SELECT student_id, AVG(num) AS avg_numFROMscoreGROUP BY student_idHAVING 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
/*SELECT student.sid, student.sname, count_course, sum_num
FROMstudentLEFT JOIN(SELECT student_id,COUNT(course_id) AS count_course,SUM(num) AS sum_numFROMscoreGROUP BY student_id) 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
/*SELECT student.sname
FROMstudent
WHEREsid NOT IN (SELECT score.student_idFROMscoreWHEREcourse_id IN (SELECT course.cidFROMcourseINNER JOINteacher ON teacher.tid = course.teacher_idWHEREteacher.tname = '李平老师'));*/# 8、 查询物理课程比生物课程分数高的学生的学号(分别得到物理成绩表与生物成绩表，然后连表即可)
/*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(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(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.caption from student inner join
(select student_id from score where num <60 group by student_id having count(course_id) >= 2) as t1 on student.sid = t1.student_id
inner join class on student.class_id = class.cid */# 11 、查询选修了所有课程的学生姓名(先从course表统计课程的总数，然后基于score表按照student_id分组，统计课程数据等于课程总数即可)
/*select sname from student where sid in (
select score.student_id from score group by score.student_id having count(score.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
/*select * 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');*/# 13、查询全部学生都选修了的,课程号和课程名(取所有学生数，然后基于score表的课程分组，找出count(student_id)等于学生数即可)
/*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
# select course_id, count(student_id) from score group by course_id ;# 15、查询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成绩并按从高到低排序（成绩去重）
# select distinct num from score order by num desc;# 17、查询平均成绩大于85的学生姓名和平均成绩
/*select sname, avg_num from student inner join
(select student_id, avg(num) as avg_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
/*select sname, num 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 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/*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 course_id ,substring_index(group_concat(student_id order by num desc),',',2) as student_info from score group by course_id ;# 21、查询不同课程但成绩相同的学号，课程号，成绩# 22、查询没学过'李平老师'课程的学生姓名以及选修的课程名称；(李平老师教物理和美术)(先查出李平老师教的所有学生，再利用差集，将学生表中是李平老师的学生排除即可)select sid, sname from student where sid not in
(select student_id from score inner join
(select cid from course inner join teacher on teacher.tid = course.teacher_id where teacher.tname ='李平老师')as t1 on score.course_id = t1.cid group by student_id);# 23、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；# 24、任课最多的老师中学生单科成绩最高的学生姓名*/权限管理
#授权表
user #该表放行的权限，针对：所有数据，所有库下所有表，以及表下的所有字段
db #该表放行的权限，针对：某一数据库，该数据库下的所有表，以及表下的所有字段
tables_priv #该表放行的权限。针对：某一张表，以及该表下的所有字段
columns_priv #该表放行的权限，针对：某一个字段#按图解释：
user：放行db1，db2及其包含的所有
db：放行db1，及其db1包含的所有
tables_priv:放行db1.table1，及其该表包含的所有
columns_prive:放行db1.table1.column1，只放行该字段权限相关操作
#创建用户
create user 'egon'@'1.1.1.1' identified by '123';
create user 'egon'@'192.168.1.%' identified by '123';
create user 'egon'@'%' identified by '123';#授权：对文件夹，对文件，对文件某一字段的权限
查看帮助：help grant
常用权限有：select,update,alter,delete
all可以代表除了grant之外的所有权限#针对所有库的授权:*.*
grant select on *.* to 'egon1'@'localhost' identified by '123'; #只在user表中可以查到egon1用户的select权限被设置为Y#针对某一数据库：db1.*
grant select on db1.* to 'egon2'@'%' identified by '123'; #只在db表中可以查到egon2用户的select权限被设置为Y#针对某一个表：db1.t1
grant select on db1.t1 to 'egon3'@'%' identified by '123'; #只在tables_priv表中可以查到egon3用户的select权限#针对某一个字段：
mysql> select * from t3;
+------+-------+------+
| id | name | age |
+------+-------+------+
| 1 | egon1 | 18 |
| 2 | egon2 | 19 |
| 3 | egon3 | 29 |
+------+-------+------+grant select (id,name),update (age) on db1.t3 to 'egon4'@'localhost' identified by '123';
#可以在tables_priv和columns_priv中看到相应的权限mysql> select * from tables_priv where user='egon4'\G
*************************** 1. row ***************************Host: localhostDb: db1User: egon4Table_name: t3Grantor: root@localhostTimestamp: 0000-00-00 00:00:00Table_priv:
Column_priv: Select,Update
row in set (0.00 sec)mysql> select * from columns_priv where user='egon4'\G
*************************** 1. row ***************************Host: localhostDb: db1User: egon4Table_name: t3
Column_name: idTimestamp: 0000-00-00 00:00:00
Column_priv: Select
*************************** 2. row ***************************Host: localhostDb: db1User: egon4Table_name: t3
Column_name: nameTimestamp: 0000-00-00 00:00:00
Column_priv: Select
*************************** 3. row ***************************Host: localhostDb: db1User: egon4Table_name: t3
Column_name: ageTimestamp: 0000-00-00 00:00:00
Column_priv: Update
rows in set (0.00 sec)#删除权限
revoke select on db1.* from 'egon'@'%';
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