mysql表操作之数据操作

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一、介绍

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

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


二、插入数据INSERT

1. 插入完整数据(顺序插入)
    语法一:
    INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n);

    语法二:
    INSERT INTO 表名 VALUES (值1,值2,值3…值n);

2. 指定字段插入数据
    语法:
    INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…);

3. 插入多条记录
    语法:
    INSERT INTO 表名 VALUES
        (值1,值2,值3…值n),
        (值1,值2,值3…值n),
        (值1,值2,值3…值n);
        
4. **插入查询结果**
    语法:
    INSERT INTO 表名(字段1,字段2,字段3…字段n) 
                    SELECT (字段1,字段2,字段3…字段n) FROM 表2
                    WHERE …;

三、更新数据UPDATE

语法:
    UPDATE 表名 SET
        字段1=1,
        字段2=2 WHERE CONDITION;

示例:
    UPDATE mysql.user SET password=password(‘123’) 
        where user=’root’ and host=’localhost’;

四、删除数据DELETE

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
    

查询数据

1. 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

2. 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 约束条件
group by  分组
having  过滤
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.将分组的结果进行having过滤

5.执行select

6.去重

7.将结果按条件排序:order by

8.限制结果的显示条数

准备表和记录

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),

(‘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),
(‘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),
(‘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)
;
#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

WHERE约束

where字句中可以使用:
1. 比较运算符:> < >= <= <> !=
2. between 80 and 100 值在10到20之间
3. in(80,90,100) 值是10或20或30
4. like ‘egon%‘
    pattern可以是%或_,
    %表示任意多字符
    _表示一个字符 
5. 逻辑运算符:在多个条件直接可以使用逻辑运算符 and or not
#1:单条件查询
    SELECT name FROM 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__‘;
  • 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9000-10000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

分组查询:GROUP BY

  1. 什么是分组?为什么要分组?
#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. GROUP_BY
  • 先确定分组的条件,然后再利用函数将其他字段的记录整合成一行即可;

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


# 求每个分类的记录个数
mysql> select depart_id,count(name) from employee group by depart_id;
+-----------+-------------+
| depart_id | count(name) |
+-----------+-------------+
|         1 |           8 |
|         2 |           5 |
|         3 |           5 |
+-----------+-------------+
3 rows in set (0.00 sec)

# 将符合类别的所有记录的名字组合成一项
mysql> select depart_id, group_concat(name) from employee group by depart_id;
+-----------+------------------------------------------------------------+
| depart_id | group_concat(name)                                         |
+-----------+------------------------------------------------------------+
|         1 | egon,alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
|         2 | 歪歪,丫丫,丁丁,星星,星星                                   |
|         3 | 张野,程咬金,程咬银,程咬铜,程咬铁                           |
+-----------+------------------------------------------------------------+
3 rows in set (0.00 sec)

# 求每个类别中的最大值
mysql> select depart_id, max(salary) from employee group by depart_id;
+-----------+-------------+
| depart_id | max(salary) |
+-----------+-------------+
|         1 |  1000000.31 |
|         2 |     3000.29 |
|         3 |    20000.00 |
+-----------+-------------+
3 rows in set (0.00 sec)

  1. 聚合函数
#强调:聚合函数聚合的是组的内容,若是没有分组,则默认一组

示例:
    SELECT COUNT(*) FROM employee;
    SELECT COUNT(*) FROM employee WHERE depart_id=1;
    SELECT MAX(salary) FROM employee;
    SELECT MIN(salary) FROM employee;
    SELECT AVG(salary) FROM employee;
    SELECT SUM(salary) FROM employee;
    SELECT SUM(salary) FROM employee WHERE depart_id=3;
  • 小练习
1. 查询岗位名以及岗位包含的所有员工名字
mysql> select post, group_concat(name) from emp group by post;

2. 查询岗位名以及各岗位内包含的员工个数
mysql> select post, count(id) from emp group by post;

3. 查询公司内男员工和女员工的个数
mysql> select sex, count(id) from emp group by sex;

4. 查询岗位名以及各岗位的平均薪资
mysql> select post, avg(salary) as ‘平均薪资‘ from emp group by post;

5. 查询岗位名以及各岗位的最高薪资
select post, max(salary) as ‘最高薪资‘ from emp group by post;

6. 查询岗位名以及各岗位的最低薪资
select post, max(salary) as ‘最高薪资‘ from emp group by post;

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 sex, avg(salary) as ‘平均薪资‘ from emp group by sex;

  1. 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
  • 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
select post, group_concat(name) as "员工姓名", count(id) as "员工数量" from emp group by post having count(id) <2;

3. 查询各岗位平均薪资大于10000的岗位名、平均工资
select post, avg(salary) from emp group by post having avg(salary)>10000 ;

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, avg(salary) from emp group by post;select post, avg(salary) from emp group by post having avg(salary) in (10000, 20000) ;

  1. 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
select * from emp order by age desc, hire_date desc;

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
# 1.对post进行分组;2.having筛选工资;3.工资排序;
select post, avg(salary) as ‘平均工资‘ from emp group by post having avg(salary)>10000 order by avg(salary);

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

  1. 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
select * from emp limit 5;
select * from emp limit 5, 5;
select * from emp limit 10, 5;
  1. 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‘;  # 准确查询
WHERE name LIKE ‘yua%‘;  # 模糊查询
WHERE name REGEXP ‘on$‘;  # 模糊查询
  • 小练习
查看所有员工中名字是jin开头,n或者g结果的员工信息
select * from emp where name regexp "^jin.*[ng]$";



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