6.分组查询,二、查询数据select

作者: www.9159.com  发布:2019-10-08

本节重点:

主要内容:

1.查询语法

2.关键字的执行优先级

3.简单查询

4.单条件查询

5.where 约束

6.分组查询: group by

7.使用聚合函数查询

8.having 过滤

9.查询排序:order by

10限制查询的记录数:limit

11.使用正则表达式查询

先建数据库(文件夹)、后表(文件)带字段,后记录(内容)。

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)

一 介绍

本节内容:

查询语法

关键字的执行优先级

简单查询

单条件查询:WHERE

分组查询:GROUP BY

HAVING

查询排序:ORDER BY

限制查询的记录数:LIMIT

使用聚合函数查询

使用正则表达式查询

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)
;

一、MYSQL数据操作(增 改 删)

  单表查询

一:查询语法:

select 字段1,字段2...  from  表名
             where  条件
             group by  field
             having   筛选
            order by field
            limit   限制条数

二 查询语法

SELECT 字段1,字段2... FROM 表名
                  WHERE 条件
                  GROUP BY field
                  HAVING 筛选
                  ORDER BY field
                  LIMIT 限制条数

 

www.9159.com 1www.9159.com 2

 

二:关键字的执行优先级(重点)

重点:关键字的优先级执行顺序
1.from
2.where
3.group by
4.having
5.select
6.distinct
7.order by
8.limit

1.找到表:from

2.拿着where指定的约束条件,去文件/表中取出一条条记录

3.将取出的一条条记录进行分组group by,如果没有group by,则整体作为一组

4.按照select后的字段得到一张新的虚拟表,如果有聚合函数,则将组内数据进行聚合

5.将4的结果过滤:having

6.查出结果:select

7.去重

8.将结果按条件排序:order by

9.限制结果的显示条数

三 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

1.找到表:from

2.拿着where指定的约束条件,去文件/表中取出一条条记录

3.将取出的一条条记录进行分组group by,如果没有group by,则整体作为一组

4.按照select后的字段得到一张新的虚拟表,如果有聚合函数,则将组内数据进行聚合

5.将4的结果过滤:having,如果有聚合函数也是先执行聚合再having过滤

6.查出结果:select

7.去重

8.将结果按条件排序:order by

9.限制结果的显示条数

[详细见:

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2
                    WHERE …;

语法:

三: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DISTINCT
    select 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;

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

www.9159.com 3www.9159.com 4

select  concat('<名字:',name,’> ' , '<薪资:',salary,'>') from employee;
select distinct depart_id from employee;
select name,salary*12 annual_salary from employee;

View Code

四 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DISTINCT
    SELECT 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;

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

www.9159.com 5www.9159.com 6

select concat('<名字:',name,'>    ','<薪资:',salary,'>') from employee;
select distinct depart_id from employee;
select name,salary*12 annual_salary from employee;

View Code

插入数据insert

www.9159.com 7

四:where  约束

强调: where是一种约束条件,mysql会拿着where指定的条件取表中取数据,而having则是在取出数据后进行过滤。

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 'aray%' 

     patterm 可以是 %或_,

   %表示任意字符, _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 employee where post = 'sale';

2.多条件查询
    select name,salary from employee where post='teacher' and salary>10000;

3.关键字查询:between and
    select name,salary from employee where salary between 10000 and 20000;
    select name,salary from employee where sal''ary not between 10000 and 20000;

4.关键字查询:is null(判断某个字段是否为null 不能用等号们需要用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。
    ps:
        执行
        update employee set post_comment='' where  id=2;
        再用上条查看,就会有结果了。

5.关键字查询: in    
    select name,salary from employee where salary=3000 or salary=3500 or salary=4000;
    select name,salary from employee where salary  in (3000,3500,4000);
    select name,salary from employee where salary not in (3000,3500,4000);

6.关键字查询:like
    通配符 '%'
    select * from employee where name like 'ar%';

    通配符: '_'
    select * from employee where name like 'ar__';

小练习:

1. 查看岗位是teacher的员工姓名、年龄
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
4. 查看岗位描述不为NULL的员工信息
5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
6. 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
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪

www.9159.com 8www.9159.com 9

1.
select name,age from employee where post ='teacher';

2.
select name,age from employee where post='teacher' and age>30;
''
3.
select name,age,salary from employee where post='teacher' and salary between 9000 adn 10000;

4.
select * from employee where post_comment is not null;

5.
select name,age,salary from employee where post='teacher' and salary  in(10000,9000,30000);

6.
select name,age,salary from employee where post='teacher' and salary not in(10000,9000,30000);

7.
select name,salary from empolyee where post='teacher' and name like 'jin%';

View Code

五 WHERE约束

强调:where是一种约束条件,mysql会拿着where指定的条件去表中取数据,而having则是在取出数据后进行过滤

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 employee
         WHERE post='sale';
    

    #2:多条件查询

     SELECT name,salary FROM employee
         WHERE post='teacher' AND salary>10000;
    

    #3:关键字BETWEEN AND

     SELECT 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null
     ps:
         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__';
    
    1. 查看岗位是teacher的员工姓名、年龄
    2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
    3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
    4. 查看岗位描述不为NULL的员工信息
    5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
    6. 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
    7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪

www.9159.com 10www.9159.com 11

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%';

View Code

www.9159.com 12www.9159.com 13

一、单表查询的语法
   SELECT 字段1,字段2... FROM 表名
                  WHERE 条件
                  GROUP BY field
                  HAVING 筛选
                  ORDER BY field
                  LIMIT 限制条数
二、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

五:分组查询: group by

大前提: 可以按照任意字段分组, 但分完组后,只能查看分组的那个字段,要想取的组内的其他字段信息,需要借助函数。

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,要获取组内的其他信息,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;  #按岗位分组,并查看成员名。
    select post,group concat(name) as emp_members from employee group by post;

group ty 与聚合函数一起使用
    select post,count(id) as count from employee group by post;  #按岗位分组,并查看每个组有多少人

强调:

如果我们用unique 的字段做为 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。

小练习:

1. 查询岗位名以及岗位包含的所有员工名字
2. 查询岗位名以及各岗位内包含的员工个数
3. 查询公司内男员工和女员工的个数
4. 查询岗位名以及各岗位的平均薪资
5. 查询岗位名以及各岗位的最高薪资
6. 查询岗位名以及各岗位的最低薪资
7. 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

www.9159.com 14www.9159.com 15

1.
select post,group_concat(name) from employee group by post;

2.
select post,count(id) from employee group by post;

3.
select sex,count(id) from employee group by sex;

4.
select post,avg(salary) from employee group by post;

5.
select post,max(salary) from employee group by post;

6.
select post,min(salary) from employee group by post;

7.
select sex,avg(salary) from employee group by sex;

View Code

六 分组查询:GROUP BY

大前提:可以按照任意字段分组,但分完组后,只能查看分组的那个字段,要想取的组内的其他字段信息,需要借助函数

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

#!!!MySQL 5.7默认ONLY_FULL_GROUP_BY语义介绍
#参考链接:http://www.ywnds.com/?p=8184
#分组查询的常见问题:
mysql> select id,count from tt group by id;
ERROR 1055 (42000): Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'test.tt.count' which is 
not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=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

#去掉ONLY_FULL_GROUP_BY模式,如下操作:
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';


#!!!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。

1. 查询岗位名以及岗位包含的所有员工名字
2. 查询岗位名以及各岗位内包含的员工个数
3. 查询公司内男员工和女员工的个数
4. 查询岗位名以及各岗位的平均薪资
5. 查询岗位名以及各岗位的最高薪资
6. 查询岗位名以及各岗位的最低薪资
7. 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

www.9159.com 16www.9159.com 17

#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 |
+--------+---------------+

View Code

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’;

1.找到表:from

六:使用聚合函数查询

先from找到表

再用where的条件约束去表中取出记录

然后进行分组group by,没有分组则默认一组

然后进行聚合

最后select出结果

示例:
    select count(*) from employee;
    select count(*) from empoloyee where depart_id=1;
    select max(salary) from emploee;
    select min(salary) from employee;
    select avg(salary) from employee;
    select sum(salary) from employee;
    select sum(salary) from employee where depart_id=3;

七 使用聚合函数查询

先from找到表

再用where的条件约束去表中取出记录

然后进行分组group by,没有分组则默认一组

然后进行聚合

最后select出结果

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;

更新数据update

2.拿着where指定的约束条件,去文件/表中取出一条条记录

七:having 过滤

having 与 where 在语法上是一样的。

select * from employee where salary > 10000;
select * from employee having salary > 10000;

不同点:

1.执行优先级:从高到低。
    where > group by > 聚合函数 > having 

2. where 是一个约束条件,是在结果返回之前起作用的。(先找到表,按where的约束条件,取出数据)
    having 是一个过滤条件,是在结果返回以后起作用的。(取出数据后,在group by 分组,如果没有group by 则所有的记录为一组,在执行聚合函数,然后使用having 对聚合的结果进行过滤),在having中可以用聚合函数,where则不能。

3.having 可以放到 group by 之后,而 where 只能放到group by 之前。

4.在查询过程中聚合语句有:
    (sum,min,max,avg,count) 要比having 子句优先执行,
    而where 子句在查询过程中执行优先级高于聚合语句。

验证不同之处:

#验证之前再次强调:执行优先级从高到低:where > group by > 聚合函数 > having 
select count(id) from employee where salary > 10000; #正确,分析:where先执行,后执行聚合count(id),然后select出结果
select count(id) from employee having salary > 10000;#错误,分析:先执行聚合count(id),后执行having过滤,无法对id进行salary>10000的过滤

#以上两条sql的顺序是
1:找到表employee--->用where过滤---->没有分组则默认一组执行聚合count(id)--->select执行查看组内id数目
2:找到表employee--->没有分组则默认一组执行聚合count(id)---->having 基于上一步聚合的结果(此时只有count(id)字段了)进行salary>10000的过滤,很明显,根本无法获取到salary字段

其他需要注意的问题:

select post,group_concat(name) from employee group by post having salary > 10000;#错误,分组后无法直接取到salary字段
select post,group_concat(name) from employee group by post having avg(salary) > 10000;

小练习:

1. 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
3. 查询各岗位平均薪资大于10000的岗位名、平均工资
4. 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资

www.9159.com 18www.9159.com 19

1.
select post,group_concat(name),count(id) from empoloyee group by post having count(id) < 2;

2.
select post,avg(salary)  from employee group by post having avg(salary) > 10000;

3.
select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) < 20000;

View Code

八 HAVING过滤

HAVING与WHERE在语法上是一样的

select * from employee where salary > 10000;
select * from employee having salary > 10000;

HAVING与WHERE不一样的地方在于!!!!!!

#!!!执行优先级从高到低:where > group by > 聚合函数 > having 
#1. Where 是一个约束声明,使用Where约束来自数据库的数据,Where是在结果返回之前起作用的(先找到表,按照where的约束条件,从表(文件)中取出数据),Where中不能使用聚合函数。

#2. Having是一个过滤声明,是在查询返回结果集以后对查询结果进行的过滤操作(先找到表,按照where的约束条件,从表(文件)中取出数据,然后group by分组,如果没有group by则所有记录整体为一组,然后执行聚合函数,然后使用having对聚合的结果进行过滤),在Having中可以使用聚合函数。

#3. having可以放到group by之后,而where只能放到group by之前

#4. 在查询过程中聚合语句(sum,min,max,avg,count)要比having子句优先执行。而where子句在查询过程中执行优先级高于聚合语句。

验证不同之处

#验证之前再次强调:执行优先级从高到低:where > group by > 聚合函数 > having 
select count(id) from employee where salary > 10000; #正确,分析:where先执行,后执行聚合count(id),然后select出结果
select count(id) from employee having salary > 10000;#错误,分析:先执行聚合count(id),后执行having过滤,无法对id进行salary>10000的过滤

#以上两条sql的顺序是
1:找到表employee--->用where过滤---->没有分组则默认一组执行聚合count(id)--->select执行查看组内id数目
2:找到表employee--->没有分组则默认一组执行聚合count(id)---->having 基于上一步聚合的结果(此时只有count(id)字段了)进行salary>10000的过滤,很明显,根本无法获取到salary字段

其他需要注意的问题

select post,group_concat(name) from employee group by post having salary > 10000;#错误,分组后无法直接取到salary字段
select post,group_concat(name) from employee group by post having avg(salary) > 10000;

 

小练习:

1. 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
3. 查询各岗位平均薪资大于10000的岗位名、平均工资
4. 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 |
+-----------+--------------+

www.9159.com 20www.9159.com 21

3.将取出的一条条记录进行分组group by,如果没有group by,则整体作为一组

八:查询排序: order by

按单列排序:
    select * from employee oeder by salary;
    select * from employee order by asc;
    select * from employee order by desc;

按多列排序:先按age排序,如果年纪相同,则按照薪资排序
    select * from employee order by age,salary desc;

小练习:

1. 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
2. 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
3. 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

www.9159.com 22www.9159.com 23

1.
select * from employee order by age asc,hire_data desc;

2.
select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;

3.
select post,avg(salary) from employee group by post having avg(salary) >10000
order bu avg(salary) desc;

View Code

九 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 employee
        ORDER BY age,
        salary DESC;

小练习:

1. 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
2. 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
3. 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

 

www.9159.com 24www.9159.com 25

#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 |
+-----------+---------------+

View Code

语法:
    DELETE FROM 表名 
        WHERE CONITION;

示例:
    DELETE FROM mysql.user 
        WHERE password=’’;

练习:
    更新MySQL root用户密码为mysql123
    删除除从本地登录的root用户以外的所有用户

4.将分组的结果进行having过滤

九: 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 DESC
        LIMIT 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 DESC
        LIMIT 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

小练习:

1. 分页显示,每页5条

www.9159.com 26www.9159.com 27

#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 |
+-----------+---------------+

回到顶部
十 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 DESC
        LIMIT 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 DESC
        LIMIT 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

小练习:
1. 分页显示,每页5条


mysql> select * from  employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name      | sex  | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
|  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 |
|  2 | alex      | male |  78 | 2015-03-02 | teacher                                 |              | 1000000.31 |    401 |         1 |
|  3 | wupeiqi   | male |  81 | 2013-03-05 | teacher                                 | NULL         |    8300.00 |    401 |         1 |
|  4 | yuanhao   | male |  73 | 2014-07-01 | teacher                                 | NULL         |    3500.00 |    401 |         1 |
|  5 | liwenzhou | male |  28 | 2012-11-01 | teacher                                 | NULL         |    2100.00 |    401 |         1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
5 rows in set (0.00 sec)

mysql> select * from  employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name       | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
|  8 | 成龙       | male   |  48 | 2010-11-11 | teacher | NULL         | 10000.00 |    401 |         1 |
|  9 | 歪歪       | female |  48 | 2015-03-11 | sale    | NULL         |  3000.13 |    402 |         2 |
| 10 | 丫丫       | female |  38 | 2010-11-01 | sale    | NULL         |  2000.35 |    402 |         2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)

mysql> select * from  employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name      | sex    | age | hire_date  | post      | post_comment | salary   | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁      | female |  18 | 2011-03-12 | sale      | NULL         |  1000.37 |    402 |         2 |
| 12 | 星星      | female |  18 | 2016-05-13 | sale      | NULL         |  3000.29 |    402 |         2 |
| 13 | 格格      | female |  28 | 2017-01-27 | sale      | NULL         |  4000.33 |    402 |         2 |
| 14 | 张野      | male   |  28 | 2016-03-11 | operation | NULL         | 10000.13 |    403 |         3 |
| 15 | 程咬金    | male   |  18 | 1997-03-12 | operation | NULL         | 20000.00 |    403 |         3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)

View Code

十 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 DESC
        LIMIT 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 DESC
        LIMIT 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

小练习:

1. 分页显示,每页5条

www.9159.com 28www.9159.com 29

mysql> select * from  employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name      | sex  | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
|  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 |
|  2 | alex      | male |  78 | 2015-03-02 | teacher                                 |              | 1000000.31 |    401 |         1 |
|  3 | wupeiqi   | male |  81 | 2013-03-05 | teacher                                 | NULL         |    8300.00 |    401 |         1 |
|  4 | yuanhao   | male |  73 | 2014-07-01 | teacher                                 | NULL         |    3500.00 |    401 |         1 |
|  5 | liwenzhou | male |  28 | 2012-11-01 | teacher                                 | NULL         |    2100.00 |    401 |         1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
rows in set (0.00 sec)

mysql> select * from  employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name       | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
|  8 | 成龙       | male   |  48 | 2010-11-11 | teacher | NULL         | 10000.00 |    401 |         1 |
|  9 | 歪歪       | female |  48 | 2015-03-11 | sale    | NULL         |  3000.13 |    402 |         2 |
| 10 | 丫丫       | female |  38 | 2010-11-01 | sale    | NULL         |  2000.35 |    402 |         2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
rows in set (0.00 sec)

mysql> select * from  employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name      | sex    | age | hire_date  | post      | post_comment | salary   | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁      | female |  18 | 2011-03-12 | sale      | NULL         |  1000.37 |    402 |         2 |
| 12 | 星星      | female |  18 | 2016-05-13 | sale      | NULL         |  3000.29 |    402 |         2 |
| 13 | 格格      | female |  28 | 2017-01-27 | sale      | NULL         |  4000.33 |    402 |         2 |
| 14 | 张野      | male   |  28 | 2016-03-11 | operation | NULL         | 10000.13 |    403 |         3 |
| 15 | 程咬金    | male   |  18 | 1997-03-12 | operation | NULL         | 20000.00 |    403 |         3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
rows in set (0.00 sec)

View Code

删除数据delete

5.执行select

十: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结果的员工信息

select * from employee where name regexp '^jin.*[gn]$';

  

 

十一 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结果的员工信息

www.9159.com 30www.9159.com 31

select * from employee where name regexp '^jin.*[gn]$';

View Code

 

 

6.去重

二、查询数据select

7.将结果按条件排序:order by

 

8.限制结果的显示条数

"""单表查询"""

 

www.9159.com 32www.9159.com 33

www.9159.com 34

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)
;

 

例 表

创建公司员工表,表的字段和数据类型

1、查询语法

www.9159.com 35

SELECT 字段1,字段2... FROM 表名
                  WHERE 条件
                  GROUP BY field
                  HAVING 筛选
                  ORDER BY field
                  LIMIT 限制条数
company.employee
    员工id          id                          int                  
    姓名            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

2、关键字的执行优先级(重点)

www.9159.com 36

www.9159.com 37www.9159.com 38

 

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

www.9159.com 39www.9159.com 40

View Code

#创建表,设置字段的约束条件
create table employee(
    id int primary key 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
    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 |
| emp_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    |                |
| salart               | double(15,2)                  | YES  |         | NULL    |                |
| office              | int(11)                           | YES  |         | NULL    |                |
| depart_id        | int(11)                           | YES  |         | NULL    |                |
+--------------+-----------------------+------+-----+---------+----------------+
10 rows in set (0.08 sec)

#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),
('xiaomage','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)
;

www.9159.com 41www.9159.com 42

创建员工表,并插入记录

1.找到表:from

2.拿着where指定的约束条件,去文件/表中取出一条条记录

3.将取出的一条条记录进行分组group by,如果没有group by,则整体作为一组

4.按照select后的字段得到一张新的虚拟表,如果有聚合函数,则将组内数据进行聚合

5.将4的结果过滤:having,如果有聚合函数也是先执行聚合再having过滤

6.查出结果:select

7.去重

8.将结果按条件排序:order by

9.限制结果的显示条数

 

详解

(1)where 约束 

 

www.9159.com 43

3、简单查询

where子句中可以使用
1.比较运算符:>、<、>=、<=、<>、!=
2.between 80 and 100 :值在80到100之间
3.in(80,90,100)值是10或20或30
4.like 'xiaomagepattern': pattern可以是%或者_。%小时任意多字符,_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

www.9159.com 44www.9159.com 45

www.9159.com 46

#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DISTINCT
    SELECT 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;

 

View Code

验证结果:

 

www.9159.com 47www.9159.com 48

4、where约束

#1 :单条件查询
mysql> select id,emp_name from employee where id > 5;
+----+------------+
| id | emp_name   |
+----+------------+
|  6 | jingliyang |
|  7 | jinxin     |
|  8 | xiaomage   |
|  9 | 歪歪       |
| 10 | 丫丫       |
| 11 | 丁丁       |
| 12 | 星星       |
| 13 | 格格       |
| 14 | 张野       |
| 15 | 程咬金     |
| 16 | 程咬银     |
| 17 | 程咬铜     |
| 18 | 程咬铁     |

#2 多条件查询
mysql> select emp_name from employee where post='teacher' and salary>10000;
+----------+
| emp_name |
+----------+
| alex         |
| jinxin     |
+----------+

#3.关键字BETWEEN AND
 SELECT name,salary FROM employee 
        WHERE salary BETWEEN 10000 AND 20000;

 SELECT name,salary FROM employee 
        WHERE salary NOT BETWEEN 10000 AND 20000;

#注意''是空字符串,不是null
 SELECT name,post_comment FROM employee WHERE post_comment='';
 ps:
        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
mysql>  SELECT name,salary FROM employee WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
+------------+---------+
| name       | salary  |
+------------+---------+
| yuanhao    | 3500.00 |
| jingliyang | 9000.00 |
+------------+---------+
2 rows in set (0.00 sec)

mysql>  SELECT name,salary FROM employee  WHERE salary IN (3000,3500,4000,9000) ;
+------------+---------+
| name       | salary  |
+------------+---------+
| yuanhao    | 3500.00 |
| jingliyang | 9000.00 |
+------------+---------+
mysql>  SELECT name,salary FROM employee  WHERE salary NOT IN (3000,3500,4000,9000) ;
+-----------+------------+
| name      | salary     |
+-----------+------------+
| egon      |    7300.33 |
| alex      | 1000000.31 |
| wupeiqi   |    8300.00 |
| liwenzhou |    2100.00 |
| jinxin    |   30000.00 |
| xiaomage  |   10000.00 |
| 歪歪      |    3000.13 |
| 丫丫      |    2000.35 |
| 丁丁      |    1000.37 |
| 星星      |    3000.29 |
| 格格      |    4000.33 |
| 张野      |   10000.13 |
| 程咬金    |   20000.00 |
| 程咬银    |   19000.00 |
| 程咬铜    |   18000.00 |
| 程咬铁    |   17000.00 |
+-----------+------------+
16 rows in set (0.00 sec)

#6:关键字LIKE模糊查询
通配符’%’
mysql> SELECT * FROM employee WHERE name LIKE 'jin%';
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name       | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
2 rows in set (0.00 sec)


通配符'_'

mysql> SELECT  age FROM employee WHERE name LIKE 'ale_';
+-----+
| age |
+-----+
|  78 |
+-----+
1 row in set (0.00 sec)

练习:
1. 查看岗位是teacher的员工姓名、年龄
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
4. 查看岗位描述不为NULL的员工信息
5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
6. 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
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪

#对应的sql语句
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%';

强调:where是一种约束条件,mysql会拿着where指定的条件去表中取数据,而having则是在取出数据后进行过滤

where约束

www.9159.com 49www.9159.com 50

 

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

(2)group by 分组查询

where字句中可以使用: 

www.9159.com 51

www.9159.com 52www.9159.com 53

#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
#1:单条件查询
    SELECT name FROM employee
        WHERE post='sale';

#2:多条件查询
    SELECT name,salary FROM employee
        WHERE post='teacher' AND salary>10000;

#3:关键字BETWEEN AND
    SELECT 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null
    ps:
        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__';

www.9159.com 54

View Code

 

 

当执行以下sql语句的时候,是以post字段查询了组中的第一条数据,没有任何意义,因为我们现在想查出当前组的多条记录。

www.9159.com, 5、分组查询:group by

www.9159.com 55

 大前提:可以按照任意字段分组,但分完组后,只能查看分组的那个字段,要想取的组内的其他字段信息,需要借助函数

mysql> select * from employee 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                                 |              | 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
如果想分组,则必须要设置全局的sql的模式为ONLY_FULL_GROUP_BY
mysql> set global sql_mode='ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)

#查看MySQL 5.7默认的sql_mode如下:
mysql> select @@global.sql_mode;
+--------------------+
| @@global.sql_mode  |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
1 row in set (0.00 sec)

mysql> exit;#设置成功后,一定要退出,然后重新登录方可生效
Bye

www.9159.com 56www.9159.com 57

www.9159.com 58

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

 

View Code

继续验证通过group by分组之后,只能查看当前字段,如果想查看组内信息,需要借助于聚合函数

www.9159.com 59www.9159.com 60

www.9159.com 61

1. 查询岗位名以及岗位包含的所有员工名字
2. 查询岗位名以及各岗位内包含的员工个数
3. 查询公司内男员工和女员工的个数
4. 查询岗位名以及各岗位的平均薪资
5. 查询岗位名以及各岗位的最高薪资
6. 查询岗位名以及各岗位的最低薪资
7. 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
mysql> select * from emp group by post;# 报错
ERROR 1054 (42S22): Unknown column 'post' in 'group statement'



mysql>  select post from employee group by post;
+-----------------------------------------+
| post                                    |
+-----------------------------------------+
| operation                               |
| sale                                    |
| teacher                                 |
| 老男孩驻沙河办事处外交大使              |
+-----------------------------------------+
4 rows in set (0.00 sec)

练习题

www.9159.com 62

www.9159.com 63www.9159.com 64

 

#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 |
+--------+---------------+

 

View Code

(3)聚合函数

 

www.9159.com 65

6、使用聚合函数查询

max()求最大值
min()求最小值
avg()求平均值
sum() 求和
count() 求总个数

#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
# 每个部门有多少个员工
select post,count(id) from employee group by post;
# 每个部门的最高薪水
select post,max(salary) from employee group by post;
# 每个部门的最低薪水
select post,min(salary) from employee group by post;
# 每个部门的平均薪水
select post,avg(salary) from employee group by post;
# 每个部门的所有薪水
select post,sum(age) from employee group by post;

先from找到表

www.9159.com 66

再用where的条件约束去表中取出记录

 

然后进行分组group by,没有分组则默认一组

www.9159.com 67www.9159.com 68

然后进行聚合

1. 查询岗位名以及岗位包含的所有员工名字
2. 查询岗位名以及各岗位内包含的员工个数
3. 查询公司内男员工和女员工的个数
4. 查询岗位名以及各岗位的平均薪资
5. 查询岗位名以及各岗位的最高薪资
6. 查询岗位名以及各岗位的最低薪资
7. 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

最后select出结果 

小练习

www.9159.com 69www.9159.com 70

 

示例:
    SELECT COUNT(*) FROM employee;
    SELECT COUNT(*) FROM employee WHERE depart_id=1;
    SELECT MAX(salary) FROM employee;      #最大
    SELECT MIN(salary) FROM employee;      #最小
    SELECT AVG(salary) FROM employee;     #平均
    SELECT SUM(salary) FROM employee;    #查总和
    SELECT SUM(salary) FROM employee WHERE depart_id=3;

 

聚合函数

(4)HAVING过滤

 

  

7、having过滤

www.9159.com 71

 HAVING与WHERE在语法上是一样的

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
select * from employee where salary > 10000;
select * from employee having salary > 10000;

www.9159.com 72

HAVING与WHERE不一样的地方在于!!!!!!

 

www.9159.com 73www.9159.com 74

验证:

#!!!执行优先级从高到低:where > group by > 聚合函数 > having 
#1. Where 是一个约束声明,使用Where约束来自数据库的数据,Where是在结果返回之前起作用的(先找到表,按照where的约束条件,
从表(文件)中取出数据),where中不能使用聚合函数。


#2. Having是一个过滤声明,是在查询返回结果集以后对查询结果进行的过滤操作(先找到表,按照where的约束条件,
从表(文件)中取出数据,然后group by分组,如果没有group by则所有记录整体为一组,然后执行聚合函数,然后使用having对聚合的结果进行过滤),
在Having中可以使用聚合函数。

#3. having可以放到group by之后,而where只能放到group by之前

#4. 在查询过程中聚合语句(sum,min,max,avg,count)要比having子句优先执行。而where子句在查询过程中执行优先级高于聚合语句。

www.9159.com 75www.9159.com 76

View Code

验证:
mysql> select * from employee where salary>1000000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex  | age | hire_date  | post    | post_comment | salary     | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
|  2 | alex | male |  78 | 2015-03-02 | teacher |              | 1000000.31 |    401 |         1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec)

mysql> select * from employee having salary>1000000;
ERROR 1463 (42000): Non-grouping field 'salary' is used in HAVING clause

# 必须使用group by才能使用group_concat()函数,将所有的name值连接
mysql> 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 'post' in 'field list'

 验证不同之处

View Code

www.9159.com 77www.9159.com 78

 

#验证之前再次强调:执行优先级从高到低:where > group by > 聚合函数 > having 
select count(id) from employee where salary > 10000; #正确,分析:where先执行,后执行聚合count(id),然后select出结果
select count(id) from employee having salary > 10000;#错误,分析:先执行聚合count(id),后执行having过滤,
                                                                无法对id进行salary>10000的过滤

#以上两条sql的顺序是
1:找到表employee--->用where过滤---->没有分组则默认一组执行聚合count(id)--->select执行查看组内id数目
2:找到表employee--->没有分组则默认一组执行聚合count(id)---->having 基于上一步聚合的结果(此时只有count(id)字段了)
进行salary>10000的过滤,很明显,根本无法获取到salary字段

小练习:

View Code

1. 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
2. 查询各岗位平均薪资大于10000的岗位名、平均工资
3. 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资

 其他需要注意的问题

 

select post,group_concat(name) from employee group by post having salary > 10000;#错误,分组后无法直接取到salary字段
select post,group_concat(name) from employee group by post having avg(salary) > 10000;

小练习答案:

 

www.9159.com 79www.9159.com 80

8、查询排序:order by

# 题1:
mysql> select post,group_concat(name),count(id) from employee group by post;
+-----------------------------------------+-----------------------------------------------------------+-----------+
| post                                    | group_concat(name)                                        | count(id) |
+-----------------------------------------+-----------------------------------------------------------+-----------+
| operation                               | 程咬铁,程咬铜,程咬银,程咬金,张野                          |         5 |
| sale                                    | 格格,星星,丁丁,丫丫,歪歪                                  |         5 |
| teacher                                 | xiaomage,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |         7 |
| 老男孩驻沙河办事处外交大使              | egon                                                      |         1 |
+-----------------------------------------+-----------------------------------------------------------+-----------+
4 rows in set (0.00 sec)

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 |
+-----------------------------------------+--------------------+-----------+
1 row in set (0.00 sec)


#题2:
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000;
+-----------+---------------+
| post      | avg(salary)   |
+-----------+---------------+
| operation |  16800.026000 |
| teacher   | 151842.901429 |
+-----------+---------------+
2 rows in set (0.00 sec)

#题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 |
+-----------+--------------+
1 row in set (0.00 sec)

www.9159.com 81www.9159.com 82

View Code

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 employee
        ORDER BY age,
        salary DESC;

 

View Code

(5)order by 查询排序

www.9159.com 83www.9159.com 84

www.9159.com 85

1. 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
2. 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
3. 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
按单列排序
    SELECT * FROM employee ORDER BY age;
    SELECT * FROM employee ORDER BY age ASC;
    SELECT * FROM employee ORDER BY age DESC;
按多列排序:先按照age升序排序,如果年纪相同,则按照id降序
    SELECT * from employee
        ORDER BY age ASC,
        id DESC;

练习

www.9159.com 86

www.9159.com 87www.9159.com 88

 

#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 |
+-----------+---------------+

www.9159.com 89www.9159.com 90

View Code

验证多列排序:
SELECT * from employee ORDER BY age ASC,id DESC;
mysql> SELECT * from employee ORDER BY age ASC,id DESC;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name       | sex    | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 18 | 程咬铁     | female |  18 | 2014-05-12 | operation                               | NULL         |   17000.00 |    403 |         3 |
| 17 | 程咬铜     | male   |  18 | 2015-04-11 | operation                               | NULL         |   18000.00 |    403 |         3 |
| 16 | 程咬银     | female |  18 | 2013-03-11 | operation                               | NULL         |   19000.00 |    403 |         3 |
| 15 | 程咬金     | male   |  18 | 1997-03-12 | operation                               | NULL         |   20000.00 |    403 |         3 |
| 12 | 星星       | female |  18 | 2016-05-13 | sale                                    | NULL         |    3000.29 |    402 |         2 |
| 11 | 丁丁       | female |  18 | 2011-03-12 | sale                                    | NULL         |    1000.37 |    402 |         2 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher                                 | NULL         |   30000.00 |    401 |         1 |
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher                                 | NULL         |    9000.00 |    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 |
| 14 | 张野       | male   |  28 | 2016-03-11 | operation                               | NULL         |   10000.13 |    403 |         3 |
| 13 | 格格       | female |  28 | 2017-01-27 | sale                                    | NULL         |    4000.33 |    402 |         2 |
|  5 | liwenzhou  | male   |  28 | 2012-11-01 | teacher                                 | NULL         |    2100.00 |    401 |         1 |
| 10 | 丫丫       | female |  38 | 2010-11-01 | sale                                    | NULL         |    2000.35 |    402 |         2 |
|  9 | 歪歪       | female |  48 | 2015-03-11 | sale                                    | NULL         |    3000.13 |    402 |         2 |
|  8 | xiaomage   | male   |  48 | 2010-11-11 | teacher                                 | NULL         |   10000.00 |    401 |         1 |
|  4 | yuanhao    | male   |  73 | 2014-07-01 | teacher                                 | NULL         |    3500.00 |    401 |         1 |
|  2 | alex       | male   |  78 | 2015-03-02 | teacher                                 |              | 1000000.31 |    401 |         1 |
|  3 | wupeiqi    | male   |  81 | 2013-03-05 | teacher                                 | NULL         |    8300.00 |    401 |         1 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.01 sec)

mysql>

 9、限制查询的记录数:limit

验证多列排序

www.9159.com 91www.9159.com 92

 

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 DESC
        LIMIT 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 DESC
        LIMIT 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

小练习:

View Code

1. 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
2. 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
3. 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 

www.9159.com 93www.9159.com 94

 

mysql> select * from  employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name      | sex  | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
|  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 |
|  2 | alex      | male |  78 | 2015-03-02 | teacher                                 |              | 1000000.31 |    401 |         1 |
|  3 | wupeiqi   | male |  81 | 2013-03-05 | teacher                                 | NULL         |    8300.00 |    401 |         1 |
|  4 | yuanhao   | male |  73 | 2014-07-01 | teacher                                 | NULL         |    3500.00 |    401 |         1 |
|  5 | liwenzhou | male |  28 | 2012-11-01 | teacher                                 | NULL         |    2100.00 |    401 |         1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
rows in set (0.00 sec)

mysql> select * from  employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name       | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
|  8 | 成龙       | male   |  48 | 2010-11-11 | teacher | NULL         | 10000.00 |    401 |         1 |
|  9 | 歪歪       | female |  48 | 2015-03-11 | sale    | NULL         |  3000.13 |    402 |         2 |
| 10 | 丫丫       | female |  38 | 2010-11-01 | sale    | NULL         |  2000.35 |    402 |         2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
rows in set (0.00 sec)

mysql> select * from  employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name      | sex    | age | hire_date  | post      | post_comment | salary   | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁      | female |  18 | 2011-03-12 | sale      | NULL         |  1000.37 |    402 |         2 |
| 12 | 星星      | female |  18 | 2016-05-13 | sale      | NULL         |  3000.29 |    402 |         2 |
| 13 | 格格      | female |  28 | 2017-01-27 | sale      | NULL         |  4000.33 |    402 |         2 |
| 14 | 张野      | male   |  28 | 2016-03-11 | operation | NULL         | 10000.13 |    403 |         3 |
| 15 | 程咬金    | male   |  18 | 1997-03-12 | operation | NULL         | 20000.00 |    403 |         3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
rows in set (0.00 sec)

www.9159.com 95www.9159.com 96

练习:分页显示,每页5条

# 题目1
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 |
+-----------+---------------+
2 rows in set (0.00 sec)

# 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 |
+-----------+---------------+
2 rows in set (0.00 sec)

mysql>

 10、使用正则表达式查询

小练习答案

www.9159.com 97www.9159.com 98

 

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$';

(5)limit  限制查询的记录数:

View Code

www.9159.com 99

www.9159.com 100www.9159.com 101

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 DESC
        LIMIT 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 DESC
        LIMIT 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
查看所有员工中名字是jin开头,n或者g结果的员工信息


select * from employee where name regexp '^jin.*[gn]$';

www.9159.com 102

练习

 

 

小练习:
分页显示,每页5条

"""**多表查询**"""

www.9159.com 103www.9159.com 104

本节主题

# 第1页数据
  mysql> select * from  employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name      | sex  | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
|  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 |
|  2 | alex      | male |  78 | 2015-03-02 | teacher                                 |              | 1000000.31 |    401 |         1 |
|  3 | wupeiqi   | male |  81 | 2013-03-05 | teacher                                 | NULL         |    8300.00 |    401 |         1 |
|  4 | yuanhao   | male |  73 | 2014-07-01 | teacher                                 | NULL         |    3500.00 |    401 |         1 |
|  5 | liwenzhou | male |  28 | 2012-11-01 | teacher                                 | NULL         |    2100.00 |    401 |         1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
5 rows in set (0.00 sec)
# 第2页数据
mysql> select * from  employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name       | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
|  8 | xiaomage   | male   |  48 | 2010-11-11 | teacher | NULL         | 10000.00 |    401 |         1 |
|  9 | 歪歪       | female |  48 | 2015-03-11 | sale    | NULL         |  3000.13 |    402 |         2 |
| 10 | 丫丫       | female |  38 | 2010-11-01 | sale    | NULL         |  2000.35 |    402 |         2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)
# 第3页数据
mysql> select * from  employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name      | sex    | age | hire_date  | post      | post_comment | salary   | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁      | female |  18 | 2011-03-12 | sale      | NULL         |  1000.37 |    402 |         2 |
| 12 | 星星      | female |  18 | 2016-05-13 | sale      | NULL         |  3000.29 |    402 |         2 |
| 13 | 格格      | female |  28 | 2017-01-27 | sale      | NULL         |  4000.33 |    402 |         2 |
| 14 | 张野      | male   |  28 | 2016-03-11 | operation | NULL         | 10000.13 |    403 |         3 |
| 15 | 程咬金    | male   |  18 | 1997-03-12 | operation | NULL         | 20000.00 |    403 |         3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)

多表连接查询

小练习答案

复合条件连接查询

 

子查询

 

www.9159.com 105www.9159.com 106

  

#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 |
+----+------------+--------+------+--------+

创建例表

 

  一、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2
    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

www.9159.com 107www.9159.com 108

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         |
+----+------------+--------+------+--------+------+--------------+

View Code

 2、内连接:只连接匹配的行

www.9159.com 109www.9159.com 110

#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;

View Code

 3,外链接之左连接:优先显示左表全部记录

www.9159.com 111www.9159.com 112

#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         |
+----+------------+--------------+

View Code

 4、外链接之右连接:优先显示右表全部记录

www.9159.com 113www.9159.com 114

#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         |
+------+-----------+--------------+

View Code

 5 全外连接:显示左右两个表全部记录

www.9159.com 115www.9159.com 116

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

View Code

 

 二、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
出公司所有部门中年龄大于25岁的员工
select employee.name,employee.age from employee,department
    where employee.dep_id = department.id
    and 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,department
    where employee.dep_id = department.id
    and age > 25
    order by age asc;

 

三、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

 1、带in关键字的子查询

www.9159.com 117www.9159.com 118

#查询employee表,但dep_id必须在department表中出现过
select * from employee
    where dep_id in
        (select id from department);

View Code

 2、带比较运算符的子查询

www.9159.com 119www.9159.com 120

#比较运算符:=、!=、>、>=、<、<=、<>
#查询平均年龄在25岁以上的部门名
select id,name from department
    where 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 employee
    where dep_id in 
        (select id from department where name='技术');

#查看不足1人的部门名
select name from department
    where id in 
        (select dep_id from employee group by dep_id having count(id) <=1);

View Code

 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

www.9159.com 121www.9159.com 122

#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)

View Code 

 

四、练习 

 init.sql文件内容

www.9159.com 123www.9159.com 124

/*
 数据导入:
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 50624
 Source Host           : localhost
 Source Database       : sqlexam

 Target Server Type    : MySQL
 Target Server Version : 50624
 File Encoding         : utf-8

 Date: 10/21/2016 06:46:46 AM
*/

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
--  Table structure for `class`
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `caption` varchar(32) NOT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `class`
-- ----------------------------
BEGIN;
INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
COMMIT;

-- ----------------------------
--  Table structure for `course`
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `cname` varchar(32) NOT NULL,
  `teacher_id` int(11) NOT NULL,
  PRIMARY KEY (`cid`),
  KEY `fk_course_teacher` (`teacher_id`),
  CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `course`
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
COMMIT;

-- ----------------------------
--  Table structure for `score`
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `student_id` int(11) NOT NULL,
  `course_id` int(11) NOT NULL,
  `num` int(11) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_score_student` (`student_id`),
  KEY `fk_score_course` (`course_id`),
  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `score`
-- ----------------------------
BEGIN;
INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
COMMIT;

-- ----------------------------
--  Table structure for `student`
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `gender` char(1) NOT NULL,
  `class_id` int(11) NOT NULL,
  `sname` varchar(32) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_class` (`class_id`),
  CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `student`
-- ----------------------------
BEGIN;
INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四');
COMMIT;

-- ----------------------------
--  Table structure for `teacher`
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
  `tid` int(11) NOT NULL AUTO_INCREMENT,
  `tname` varchar(32) NOT NULL,
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `teacher`
-- ----------------------------
BEGIN;
INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

View Code

 从init.sql文件中导入数据

#准备表、记录
mysql> create database db1;
mysql> use db1;
mysql> source  E:\init.sql  #绝对路径

 

 !!!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

www.9159.com 125www.9159.com 126

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
、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

题目

 参考答案:http://www.cnblogs.com/wupeiqi/articles/5748496.html

 

 

本文由9159.com发布于www.9159.com,转载请注明出处:6.分组查询,二、查询数据select

关键词:

上一篇:www.9159.com:-听音乐吗,有的人善于合作
下一篇:没有了