MySQL表的CRUD及多表查询

数据库表的增删改查操作：

　　增、删、改

　　查：

　　　　单表查询

　　　　　　简单查询、where约束、group by分组、聚合查询、having过滤、order by排序、limit限制、正则匹配

　　　　多表查询

　　　　　　连表查询：交叉查询、>內连查询、左外连接查询、右外连接查询、全外链接查询、连接结果筛选查询　　　　　　　　

　　　　　　子查询　：带关键字in的子查询、带比较运算符的子查询、带关键字exists的布尔判断结果查询　

 

表记录增删改总结：

MySQL数据操作： DML

在MySQL管理软件中，可以通过SQL语句中的DML语言来实现数据的操作，包括

1. 使用INSERT实现数据的插入
2. UPDATE实现数据的更新
3. 使用DELETE实现数据的删除
4. 使用SELECT查询数据以及。　　　 

#增insert into：
    （1）单条插入
        insert into 表名 value(值1,值2,...);
    （2）多条插入
        insert into 表名 values(值1,值2,...),(值1,值2,...),...;
    （3）指定字段插入
        insert into 表名(字段1,字段2,字段3,...) values(值1,值2,值3,...);
    （4）查询结果插入
        insert into 表名(字段1,字段2,字段3,...) select (字段1,字段2,字段3,...) from 表名1;
#删delete from：
    （1）清空列表
        delete from 表名;
    （2）删除某条记录
        delete from 表名 where 条件;
#改update set：
    （1）更新数据
        update 表名 set 字段=值 where 条件;

 增：　　

（1）单条插入
        insert into 表名 value(值1,值2,...);
（2）多条插入
        insert into 表名 values(值1,值2,...),(值1,值2,...),...;
（3）指定字段插入
        insert into 表名(字段1,字段2,字段3,...) values(值1,值2,值3,...);
（4）查询结果插入
        insetr into 表名(字段1,字段2,字段3,...) select (字段1,字段2,字段3,...) from 表名1;

删：　　

删delete from：
    （1）清空列表
        delete from 表名;
    （2）删除某条记录
        delete from 表名 where 条件;

改：　　

改update set：
    （1）更新数据
        update 表名 set 字段=值 where 条件;
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’;

单表查： 　　

查select from：
    （1）单表查询语法：
        select distinct 字段1，字段2... from  表名
                                                    where 条件
                                                    group by 字段
                                                    having  条件
                                                    order by 字段[asc/desc]
                                                    limit n/m,n

    （2）执行优先级：from>where>group by>select>having>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.执行select（去重）
        5.将分组的结果进行having过滤
        6.将结果按条件排序：order by
        7.限制结果的显示条数limit

    （3）简单查询：
        1.重命名查询as:
            select * from 表名
            select 字段 as 自定义字段名 from 表名
        2.去重查询distinct：
            select distinct 字段 from 表名
        3.四则运算查询+-*/%等：
            select 字段*n from 表名;
        4.定义格式查询concat：
            select concat('字符串',字段1,'字符串',字段2...) from 表名;
            select concat_ws('连接字符串',字段1，字段2 ,...) from 表名;


    (4)where约束条件：
        1.比较运算：>,<,=,>=,<=,!=,<>
        2.between m and n  m到n之间的值（包括m、n）
        3.in（a,b,c...）   在a,b,c...中的值
        4.逻辑运算：and、or 、not
        5.模糊条件 like '%'/'_'      通配符：%表示任意个字符；  _下划线表示一个字符

    （5）group by 分组：
        分组查询获取其他字段：
            GROUP BY关键字和GROUP_CONCAT()函数一起使用
    （6）having过滤：
        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
    （7）order by排序：
        asc 顺序  desc 逆序
    （8）limit限制条数
        limit n #默认初始位置为0 取n个
        limit m,n #从m开始，往后取n个

    （9）聚合函数：
        聚合函数聚合的是组的内容，若是没有分组，则默认一组。
        count()        max()        min()        avg()        sum()

查select from：
    （1）单表查询语法：
        select distinct 字段1，字段2... from  表名
                                                    where 条件
                                                    group by 字段
                                                    having  条件
                                                    order by 字段[asc/desc]
                                                    limit n/m,n

    （2）执行优先级：from>where>group by>select>having>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.执行select（去重）
        5.将分组的结果进行having过滤
        6.将结果按条件排序：order by
        7.限制结果的显示条数limit

　单表数据准备：　

company.employee
    员工id      id                  int
    姓名        emp_name            varchar
    性别        sex                 enum
    年龄        age                 int
    入职日期     hire_date           date
    岗位        post                varchar
    职位描述     post_comment        varchar
    薪水        salary              double
    办公室       office              int
    部门编号     depart_id           int



#创建表
create table employee(
id int not null unique auto_increment,
emp_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 |
| 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    |                |
| 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(emp_name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','教学部门',7300.33,401,1), #以下是教学部
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龙','male',48,'20101111','teacher',10000,401,1),

('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('丫丫','female',38,'20101101','sale',2000.35,402,2),
('丁丁','female',18,'20110312','sale',1000.37,402,2),
('星星','female',18,'20160513','sale',3000.29,402,2),
('格格','female',28,'20170127','sale',4000.33,402,2),

('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬银','female',18,'20130311','operation',19000,403,3),
('程咬铜','male',18,'20150411','operation',18000,403,3),
('程咬铁','female',18,'20140512','operation',17000,403,3)
;

#ps：如果在windows系统中，插入中文字符，select的结果为空白，可以将所有字符编码统一设置成gbk

　　简单查询：

#简单查询
    SELECT id,emp_name,sex,age,hire_date,post,post_comment,salary,office,depart_id 
    FROM employee;

    SELECT * FROM employee;

    SELECT emp_name,salary FROM employee;

#避免重复DISTINCT
    SELECT DISTINCT post FROM employee;    

#通过四则运算查询
    SELECT emp_name, salary*12 FROM employee;
    SELECT emp_name, salary*12 AS Annual_salary FROM employee;
    SELECT emp_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: ',emp_name,'  年薪: ', salary*12)  AS Annual_salary 
   FROM employee;
   
   CONCAT_WS() 第一个参数为分隔符
   SELECT CONCAT_WS(':',emp_name,salary*12)  AS Annual_salary 
   FROM employee;

   结合CASE语句：
   SELECT
       (
           CASE
           WHEN emp_name = 'jingliyang' THEN
               emp_name
           WHEN emp_name = 'alex' THEN
               CONCAT(emp_name,'_BIGSB')
           ELSE
               concat(emp_name, 'SB')
           END
       ) as new_name
   FROM
       employee;

# 1 查出所有员工的名字，薪资,格式为
#     <名字:egon>    <薪资:3000>
# 2 查出所有的岗位（去掉重复）
# 3 查出所有员工名字，以及他们的年薪,年薪的字段名为annual_year
'''
# select concat('<名字：',emp_name,'>','<薪资：',salary,'>') from employee;
# select concat('<名字：',emp_name,'>'),concat('<薪资：',salary,'>') from employee;
# select distinct post from employee;
# select emp_name,salary*12 as annual_year from employee;
'''

 

　  where约束：　

where字句中可以使用：

　　1. 比较运算符：> < >= <= <> !=
　　2. between 80 and 100 值在80到100之间
　　3. in(80,90,100) 值是80或90或100
　　4. like 'e%'
   　　 通配符可以是%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 emp_name FROM employee
        WHERE post='sale';
        
#2:多条件查询
    SELECT emp_name,salary FROM employee
        WHERE post='teacher' AND salary>10000;

#3:关键字BETWEEN AND
    SELECT emp_name,salary FROM employee 
        WHERE salary BETWEEN 10000 AND 20000;

    SELECT emp_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 emp_name,post_comment FROM employee 
        WHERE post_comment IS NULL;

    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment IS NOT NULL;
        
    SELECT emp_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 emp_name,salary FROM employee 
        WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
    
    SELECT emp_name,salary FROM employee 
        WHERE salary IN (3000,3500,4000,9000) ;

    SELECT emp_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 emp_name LIKE 'eg%';

    通配符’_’
    SELECT * FROM employee 
            WHERE emp_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
'''
# select emp_name,age from employee where post='teacher';
# select emp_name,age from employee where post='teacher' and age>30;
# select emp_name,age,salary from employee where post='teacher' and salary between 1000 and 9000;
# select *from employee where post_comment is not null;
# select emp_name,age,salary from employee where post='teacher' and salary in(10000,9000,30000);
# select emp_name,age,salary from employee where post='teacher' and salary  not in (10000,9000,30000);
# select emp_name,salary*12 as annul_salary from employee where post='teacher' and emp_name like 'jin%';
'''

 　　group by 分组：　　

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(emp_name) FROM employee GROUP BY post;#按照岗位分组，并查看组内成员名
    SELECT post,GROUP_CONCAT(emp_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

　　聚合函数：

　　#强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组

#强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组

示例：
    SELECT COUNT(*) FROM employee;
    SELECT COUNT(*) FROM employee WHERE depart_id=1;
    SELECT MAX(salary) FROM employee;
    SELECT MIN(salary) FROM employee;
    SELECT AVG(salary) FROM employee;
    SELECT SUM(salary) FROM employee;
    SELECT SUM(salary) FROM employee WHERE depart_id=3;

# 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
'''
# select post,group_concat(emp_name)from employee group by post;
# select post,count(emp_name)from employee group by post;
# select sex,count(emp_name)from employee group by sex;
# select post,group_concat(salary)from employee group by post;
# select post,avg(salary)from employee group by post;
# select post,max(salary)from employee group by post;
# select post,min(salary)from employee group by post;
# select sex,avg(salary)from employee group by sex;

　　having过滤：

#！！！执行优先级从高到低：where > group by > having 
#1. Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。
#2. Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数

mysql> select @@sql_mode;
+--------------------+
| @@sql_mode         |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
row in set (0.00 sec)

mysql> select * from emp where salary > 100000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | emp_name | sex  | age | hire_date  | post    | post_comment | salary     | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
|  2 | alex | male |  78 | 2015-03-02 | teacher | NULL         | 1000000.31 |    401 |         1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
row in set (0.00 sec)

mysql> select post,group_concat(emp_name) from emp group by post having salary > 10000;#错误，分组后无法直接取到salary字段
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
mysql> select post,group_concat(emp_name) from emp group by post having avg(salary) > 10000;
+-----------+-------------------------------------------------------+
| post | group_concat(emp_name) |
+-----------+-------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
+-----------+-------------------------------------------------------+
rows in set (0.00 sec)

# 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
'''
# select post, group_concat(emp_name),  count(emp_name) from employee group by post having count(emp_name)<2;
# select post,avg(salary) from employee group by post having avg(salary)>10000;
# select post,avg(salary) from employee group by post having 20000>avg(salary) and avg(salary)>10000;

 　　order by  排序　　

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;

# 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
'''
# select * from employee order by age,hire_date desc;
# select post,avg(salary)as avg_salary from employee group by post having avg(salary)>10000 order by avg_salary;
# select post,avg(salary)as avg_salary from employee group by post having avg(salary)>10000 order by avg_salary desc;
'''

　　limit 限制　

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

 　　使用正则表达式查询 

SELECT * FROM employee WHERE emp_name REGEXP '^ale';

SELECT * FROM employee WHERE emp_name REGEXP 'on$';

SELECT * FROM employee WHERE emp_name REGEXP 'm{2}';


小结：对字符串匹配的方式
WHERE emp_name = 'egon';
WHERE emp_name LIKE 'yua%';
WHERE emp_name REGEXP 'on$';

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 emp_name regexp '^jin.*[gn]$';

 单表操作实例：（对日期的处理可以使用year(日期字段)）　　

'''
书名 作者 出版社 价格 出版日期(publish_date)
倚天屠龙记 egon 北京工业地雷出版社 70 2019-7-1
九阳神功 alex 人民音乐不好听出版社 5 2018-7-4
九阴真经 yuan 北京工业地雷出版社 62 2017-7-12
九阴白骨爪 jin 人民音乐不好听出版社 40 2019–8-7
独孤九剑 alex 北京工业地雷出版社 12 2017-9-1
降龙十巴掌 egon 知识产权没有用出版社 20 2019-7-5
葵花宝典 yuan 知识产权没有用出版社 33 2019–8-2

0.建表book，并向表中插入数据
1.查询egon写的所有书和价格
2.找出最贵的图书的价格
3.求所有图书的均价
4.将所有图书按照出版日期排序
5.查询alex写的所有书的平均价格
6.查询人民音乐不好听出版社出版的所有图书
7.查询人民音乐出版社出版的alex写的所有图书和价格
8.找出出版图书均价最高的作者
9.找出最新出版的图书的作者和出版社
10.显示各出版社出版的所有图书
11.查找价格最高的图书，并将它的价格修改为50元
12.删除价格最低的那本书对应的数据
13.将所有alex写的书作业修改成alexsb
14.select year(publish_date) from book
自己研究上面sql语句中的year函数的功能，完成需求：
将所有2017年出版的图书从数据库中删除

'''


# create table book(id int primary key auto_increment,
#     b_name char(16),
#     b_author char(8),
#     b_press varchar(24),
#     b_price float(5,2),
#     publish_date date
#     );


# insert into book(b_name,b_author,b_press,b_price,publish_date) values
#     ('倚天屠龙记','egon','北京工业地雷出版社',70,'2019-7-1'),
#     ('九阳神功','alex','人民音乐不好听出版社',5,'2018-7-4'),
#     ('九阴真经','yuan','北京工业地雷出版社',62,'2017-7-12'),
#     ('九阴白骨爪','jin','人民音乐不好听出版社',40,'2019-8-7'),
#     ('孤独九剑','alex','北京工业地雷出版社',12,'2017-9-1'),
#     ('降龙十八掌','egon','知识产权没有用出版社',20,'2019-7-5'),
#     ('葵花宝典','yuan','知识产权没有用出版社',33,'2019-8-2');
'''
mysql> select * from book;
    +----+-----------------+----------+--------------------------------+---------+--------------+
    | id | b_name          | b_author | b_press                        | b_price | publish_date |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    |  1 | 倚天屠龙记      | egon     | 北京工业地雷出版社             |   70.00 | 2019-07-01   |
    |  2 | 九阳神功        | alex     | 人民音乐不好听出版社           |    5.00 | 2018-07-04   |
    |  3 | 九阴真经        | yuan     | 北京工业地雷出版社             |   62.00 | 2017-07-12   |
    |  4 | 九阴白骨爪      | jin      | 人民音乐不好听出版社           |   40.00 | 2019-08-07   |
    |  5 | 孤独九剑        | alex     | 北京工业地雷出版社             |   12.00 | 2017-09-01   |
    |  6 | 降龙十八掌      | egon     | 知识产权没有用出版社           |   20.00 | 2019-07-05   |
    |  7 | 葵花宝典        | yuan     | 知识产权没有用出版社           |   33.00 | 2019-08-02   |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    7 rows in set (0.00 sec)
'''

# select b_name,b_price from book where b_author='egon';
'''
mysql> select b_name,b_price from book where b_author='egon';
    +-----------------+---------+
    | b_name          | b_price |
    +-----------------+---------+
    | 倚天屠龙记      |   70.00 |
    | 降龙十八掌      |   20.00 |
    +-----------------+---------+
    2 rows in set (0.01 sec)
'''

# select max(b_price) from book;
'''
mysql> select max(b_price) from book;
    +--------------+
    | max(b_price) |
    +--------------+
    |        70.00 |
    +--------------+
    1 row in set (0.01 sec)
'''

# select avg(b_price) as avg_price from book;
'''
mysql> select avg(b_price) as avg_price from book;
    +-----------+
    | avg_price |
    +-----------+
    | 34.571429 |
    +-----------+
    1 row in set (0.00 sec)
'''

# select * from book order by publish_date;
'''
mysql> select * from book order by publish_date;
    +----+-----------------+----------+--------------------------------+---------+--------------+
    | id | b_name          | b_author | b_press                        | b_price | publish_date |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    |  3 | 九阴真经        | yuan     | 北京工业地雷出版社             |   62.00 | 2017-07-12   |
    |  5 | 孤独九剑        | alex     | 北京工业地雷出版社             |   12.00 | 2017-09-01   |
    |  2 | 九阳神功        | alex     | 人民音乐不好听出版社           |    5.00 | 2018-07-04   |
    |  1 | 倚天屠龙记      | egon     | 北京工业地雷出版社             |   70.00 | 2019-07-01   |
    |  6 | 降龙十八掌      | egon     | 知识产权没有用出版社           |   20.00 | 2019-07-05   |
    |  7 | 葵花宝典        | yuan     | 知识产权没有用出版社           |   33.00 | 2019-08-02   |
    |  4 | 九阴白骨爪      | jin      | 人民音乐不好听出版社           |   40.00 | 2019-08-07   |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    7 rows in set (0.01 sec)
'''

# select b_author,avg(b_price) from book where b_author='alex';
'''
mysql> select b_author,avg(b_price) from book where b_author='alex';
    +----------+--------------+
    | b_author | avg(b_price) |
    +----------+--------------+
    | alex     |     8.500000 |
    +----------+--------------+
    1 row in set (0.00 sec)
'''

# select b_press,group_concat(b_name) from book where b_press='人民音乐不好听出版社' group by b_press;
'''
    +--------------------------------+------------------------------+
    | b_press                        | group_concat(b_name)         |
    +--------------------------------+------------------------------+
    | 人民音乐不好听出版社           | 九阳神功,九阴白骨爪          |
    +--------------------------------+------------------------------+
    1 row in set (0.00 sec)
'''

# select  b_press,b_author,b_name,b_price from book where b_press='人民音乐不好听出版社' and b_author='alex';
'''
mysql> select  b_press,b_author,b_name,b_price from book where b_press='人民音乐不好听出版社' and b_author='alex';
    +--------------------------------+----------+--------------+---------+
    | b_press                        | b_author | b_name       | b_price |
    +--------------------------------+----------+--------------+---------+
    | 人民音乐不好听出版社           | alex     | 九阳神功     |    5.00 |
    +--------------------------------+----------+--------------+---------+
    1 row in set (0.00 sec)
'''

# select b_author,avg(b_price) from book group by b_author having avg(b_price) order by avg(b_price) desc limit 1;
'''
mysql> select b_author,avg(b_price) from book group by b_author having avg(b_price) order by avg(b_price) desc limit 1;
    +----------+--------------+
    | b_author | avg(b_price) |
    +----------+--------------+
    | yuan     |    47.500000 |
    +----------+--------------+
    1 row in set (0.00 sec)
'''


# select b_press,group_concat(b_name)as press_books from book group by b_press;
'''
mysql> select b_press,group_concat(b_name)as press_books from book group by b_press;
    +--------------------------------+-------------------------------------------+
    | b_press                        | press_books                               |
    +--------------------------------+-------------------------------------------+
    | 人民音乐不好听出版社           | 九阳神功,九阴白骨爪                       |
    | 北京工业地雷出版社             | 倚天屠龙记,九阴真经,孤独九剑              |
    | 知识产权没有用出版社           | 降龙十八掌,葵花宝典                       |
    +--------------------------------+-------------------------------------------+
    3 rows in set (0.00 sec)
'''


# select max(b_price) from book;
# update book  set b_price=50 where b_price=70.0 ;
#update book  set b_price=50 order by b_price desc limit 1;#( 只能设置一个)
'''
mysql> select * from book;
    +----+-----------------+----------+--------------------------------+---------+--------------+
    | id | b_name          | b_author | b_press                        | b_price | publish_date |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    |  1 | 倚天屠龙记      | egon     | 北京工业地雷出版社             |   50.00 | 2019-07-01   |
    |  2 | 九阳神功        | alex     | 人民音乐不好听出版社           |    5.00 | 2018-07-04   |
    |  3 | 九阴真经        | yuan     | 北京工业地雷出版社             |   62.00 | 2017-07-12   |
    |  4 | 九阴白骨爪      | jin      | 人民音乐不好听出版社           |   40.00 | 2019-08-07   |
    |  5 | 孤独九剑        | alex     | 北京工业地雷出版社             |   12.00 | 2017-09-01   |
    |  6 | 降龙十八掌      | egon     | 知识产权没有用出版社           |   20.00 | 2019-07-05   |
    |  7 | 葵花宝典        | yuan     | 知识产权没有用出版社           |   33.00 | 2019-08-02   |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    7 rows in set (0.00 sec)
'''

# select min(b_price) from book;
# delete from book where b_price=5;
'''
mysql> select * from book;
    +----+-----------------+----------+--------------------------------+---------+--------------+
    | id | b_name          | b_author | b_press                        | b_price | publish_date |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    |  1 | 倚天屠龙记      | egon     | 北京工业地雷出版社             |   50.00 | 2019-07-01   |
    |  3 | 九阴真经        | yuan     | 北京工业地雷出版社             |   62.00 | 2017-07-12   |
    |  4 | 九阴白骨爪      | jin      | 人民音乐不好听出版社           |   40.00 | 2019-08-07   |
    |  5 | 孤独九剑        | alex     | 北京工业地雷出版社             |   12.00 | 2017-09-01   |
    |  6 | 降龙十八掌      | egon     | 知识产权没有用出版社           |   20.00 | 2019-07-05   |
    |  7 | 葵花宝典        | yuan     | 知识产权没有用出版社           |   33.00 | 2019-08-02   |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    6 rows in set (0.00 sec)
'''

# update book set b_author='alexsb' where b_author='alex';
'''
mysql>  select * from book;
    +----+-----------------+----------+--------------------------------+---------+--------------+
    | id | b_name          | b_author | b_press                        | b_price | publish_date |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    |  1 | 倚天屠龙记      | egon     | 北京工业地雷出版社             |   50.00 | 2019-07-01   |
    |  3 | 九阴真经        | yuan     | 北京工业地雷出版社             |   62.00 | 2017-07-12   |
    |  4 | 九阴白骨爪      | jin      | 人民音乐不好听出版社           |   40.00 | 2019-08-07   |
    |  5 | 孤独九剑        | alexsb   | 北京工业地雷出版社             |   12.00 | 2017-09-01   |
    |  6 | 降龙十八掌      | egon     | 知识产权没有用出版社           |   20.00 | 2019-07-05   |
    |  7 | 葵花宝典        | yuan     | 知识产权没有用出版社           |   33.00 | 2019-08-02   |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    6 rows in set (0.00 sec)
'''

# select year(publish_date) from book
'''
mysql> select year(publish_date) from book;
    +--------------------+
    | year(publish_date) |
    +--------------------+
    |               2019 |
    |               2017 |
    |               2019 |
    |               2017 |
    |               2019 |
    |               2019 |
    +--------------------+
    6 rows in set (0.00 sec)
'''


# delete from book where year(publish_date)=2017;
'''
mysql> delete from book where year(publish_date)=2017;
    Query OK, 2 rows affected (0.00 sec)

mysql> select * from book;
    +----+-----------------+----------+--------------------------------+---------+--------------+
    | id | b_name          | b_author | b_press                        | b_price | publish_date |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    |  1 | 倚天屠龙记      | egon     | 北京工业地雷出版社             |   50.00 | 2019-07-01   |
    |  4 | 九阴白骨爪      | jin      | 人民音乐不好听出版社           |   40.00 | 2019-08-07   |
    |  6 | 降龙十八掌      | egon     | 知识产权没有用出版社           |   20.00 | 2019-07-05   |
    |  7 | 葵花宝典        | yuan     | 知识产权没有用出版社           |   33.00 | 2019-08-02   |
    +----+-----------------+----------+--------------------------------+---------+--------------+
    4 rows in set (0.00 sec)
'''

 

多表查：

连表查询
    表和表是怎么连在一起的
        通过笛卡尔积得到一个全量拼接的大表
        select * from 表1，表2；两个表的记录会完全拼接

    内连接(inner join) 双方能够互相匹配的项才会被显示出来
        select * from 表1 inner join 表2 [as 新表名]  on 条件；


    外连接
        左外连接(left join) 只完整的显示左表中的所有内容,以及右表中与左表匹配的项
            select * from 表1 left join 表2 on 条件;

        右外连接(right join) 只完整的显示右表中的所有内容,以及左表中与右表匹配的项
            select * from 表1 right join 表2 on 条件;

        全外连接 永远显示左表和右表中所有的项
            select * from 表1 left join 表2  on 条件
            union
            select * from 表1 right join 表2 on 条件;

子查询(效率低)
    总是在一个select中 套着另一个select语句
        嵌套着的这个select语句就是一个子查询语句

 

 多表数据准备：

　　employee表中的dep_id可以设置外键关联到department表

#建表
create table department(
id int,
name varchar(20) 
);

create table employee(
id int primary key auto_increment,
name varchar(20),
sex enum('male','female') not null default 'male',
age int,
dep_id int
);

#插入数据
insert into department values
(200,'技术'),
(201,'人力资源'),
(202,'销售'),
(203,'运营');

insert into employee(name,sex,age,dep_id) values
('egon','male',18,200),
('alex','female',48,201),
('wupeiqi','male',38,201),
('yuanhao','female',28,202),
('liwenzhou','male',18,200),
('jingliyang','female',18,204)
;


#查看表结构和数据
mysql> desc department;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+

mysql> desc employee;
+--------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | YES | | NULL | |
| sex | enum('male','female') | NO | | male | |
| age | int(11) | YES | | NULL | |
| dep_id | int(11) | YES | | NULL | |
+--------+-----------------------+------+-----+---------+----------------+

mysql> select * from department;
+------+--------------+
| id | name |
+------+--------------+
| 200 | 技术 |
| 201 | 人力资源 |
| 202 | 销售 |
| 203 | 运营 |
+------+--------------+

mysql> select * from employee;
+----+------------+--------+------+--------+
| id | name | sex | age | dep_id |
+----+------------+--------+------+--------+
| 1 | egon | male | 18 | 200 |
| 2 | alex | female | 48 | 201 |
| 3 | wupeiqi | male | 38 | 201 |
| 4 | yuanhao | female | 28 | 202 |
| 5 | liwenzhou | male | 18 | 200 |
| 6 | jingliyang | female | 18 | 204 |
+----+------------+--------+------+--------+

连表查询

SELECT 字段列表
    FROM 表1 INNER|LEFT|RIGHT JOIN 表2 [as 新表名]  
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　　

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

　　2 内连接：只连接匹配的行

#找两张表共有的部分，相当于利用条件从笛卡尔积结果中筛选出了正确的结果
#department没有204这个部门，因而employee表中关于204这条员工信息没有匹配出来
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee inner join department on employee.dep_id=department.id; 
+----+-----------+------+--------+--------------+
| id | name      | age  | sex    | name         |
+----+-----------+------+--------+--------------+
|  1 | egon      |   18 | male   | 技术         |
|  2 | alex      |   48 | female | 人力资源     |
|  3 | wupeiqi   |   38 | male   | 人力资源     |
|  4 | yuanhao   |   28 | female | 销售         |
|  5 | liwenzhou |   18 | male   | 技术         |
+----+-----------+------+--------+--------------+

#上述sql等同于
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id=department.id;

　　3 外链接之左连接：优先显示左表全部记录 

#以左表为准，即找出所有员工信息，当然包括没有部门的员工
#本质就是：在内连接的基础上增加左边有右边没有的结果
mysql> select employee.id,employee.name,department.name as depart_name from employee left join department on employee.dep_id=department.id;
+----+------------+--------------+
| id | name       | depart_name  |
+----+------------+--------------+
|  1 | egon       | 技术         |
|  5 | liwenzhou  | 技术         |
|  2 | alex       | 人力资源     |
|  3 | wupeiqi    | 人力资源     |
|  4 | yuanhao    | 销售         |
|  6 | jingliyang | NULL         |
+----+------------+--------------+

　　4 外链接之右连接：优先显示右表全部记录

#以右表为准，即找出所有部门信息，包括没有员工的部门
#本质就是：在内连接的基础上增加右边有左边没有的结果
mysql> select employee.id,employee.name,department.name as depart_name from employee right join department on employee.dep_id=department.id;
+------+-----------+--------------+
| id   | name      | depart_name  |
+------+-----------+--------------+
|    1 | egon      | 技术         |
|    2 | alex      | 人力资源     |
|    3 | wupeiqi   | 人力资源     |
|    4 | yuanhao   | 销售         |
|    5 | liwenzhou | 技术         |
| NULL | NULL      | 运营         |
+------+-----------+--------------+

　　5 全外连接：显示左右两个表全部记录

全外连接：在内连接的基础上增加左边有右边没有的和右边有左边没有的结果
#注意：mysql不支持全外连接 full JOIN
#强调：mysql可以使用此种方式间接实现全外连接
select * from employee left join department on employee.dep_id = department.id
union
select * from employee right join department on employee.dep_id = department.id
;
#查看结果
+------+------------+--------+------+--------+------+--------------+
| id   | name       | sex    | age  | dep_id | id   | name         |
+------+------------+--------+------+--------+------+--------------+
|    1 | egon       | male   |   18 |    200 |  200 | 技术         |
|    5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
|    2 | alex       | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
|    6 | jingliyang | female |   18 |    204 | NULL | NULL        |
| NULL | NULL       | NULL   | NULL |   NULL |  203 | 运营         |
+------+------------+--------+------+--------+------+--------------+

#注意 union与union all的区别：union会去掉相同的纪录

　　6.符合条件连接查询　　

#示例1：以内连接的方式查询employee和department表，并且employee表中的age字段值必须大于25,即找出年龄大于25岁的员工以及员工所在的部门
select employee.name,department.name from employee inner join department
    on employee.dep_id = department.id
    where 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;

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　

#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(子查询得到的是有人的部门id)
select name from department where id not in (select distinct dep_id from employee);

 　　 2 .带比较运算符的子查询 

#比较运算符：=、!=、>、>=、<、<=、<>
#查询大于所有人平均年龄的员工名与年龄
mysql> select name,age from emp where age > (select avg(age) from emp);
+---------+------+
| name    | age  |
+---------+------+
| alex    | 48   |
| wupeiqi | 38   |
+---------+------+
rows in set (0.00 sec)


#查询大于部门内平均年龄的员工名、年龄(省略了重命名关键字as)
select t1.name,t1.age from emp t1
inner join 
(select dep_id,avg(age) avg_age from emp group by dep_id) t2
on t1.dep_id = t2.dep_id
where t1.age > t2.avg_age;

 　　3. 带EXISTS关键字的子查询

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

#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)