mysql数据操作之单表查询

一：介绍

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。

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)；
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n)，
    (值1，值2，值n)，
    (值1，值2，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UPDATAE

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’;

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

五：查询数据select

#1:单表查询

一 单表查询的语法：

  select distinct 查询字段1，查询字段2，。。。 from 表名
        where 分组之前的过滤条件
        group by 分组依据
        having 分组之后的过滤条件
        order by 排序字段
        limit 显示的条数;

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

1、找到表：from

2、拿着where指定的约束条件，取文件／表取出一条条记录

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、将结果按照条件排序；order by

8、限制结果的显示条数

三：简单查询

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

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
);

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

三个部门：教学，销售，运营
insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','老男孩驻沙河办事处外交大使',7300.33,401,1), #以下是教学部
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龙','male',48,'20101111','teacher',10000,401,1),

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

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

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

#简单查询
    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;

   结合CASE语句：
   SELECT
       (
           CASE
           WHEN NAME = 'egon' THEN
               NAME
           WHEN NAME = 'alex' THEN
               CONCAT(name,'_BIGSB')
           ELSE
               concat(NAME, 'SB')
           END
       ) as new_name
   FROM
       emp;

1、where过滤

select id, name from db39.emp where id >=3 and id <=6
select * from db39.emp where id between 3 and 6;


select * from emp where salary =20000 or salary =18000 or salary =17000;
select * from emperor where salary in (20000,18000,17000);


 要求：查询员工姓名中包含i字母的员工姓名与其薪资
select  name, salary  from db39.emp where name like '%I%'
要求：查询员工姓名是由四个字符组成的员工姓名与其薪资
 select name,salary from db39.emp where name like '____';
 select name,salary from db39.emp where char_length(name) = 4;

select *  from db39.emp where id not between 3 and 6;
select * from emp where salary not in (20000,18000,17000);
要求：查询岗位描述为空的员工名与岗位名
select name,post from db39.emp where post_comment is NULL;
select name,post from db39.emp where post_comment is not NULL;

2、group by分组

#设置sql_mode为only_full_group_by，意味着以后但凡分组，只能取到分组的依据
    mysql> set global sql_mode="strict_trans_tables,only_full_group_by";

    #每个部门的最高工资
    select post,max(salary) from emp group by post;
    select post,min(salary) from emp group by post;
    select post,avg(salary) from emp group by post;
    select post,sum(salary) from emp group by post;
    select post,count(id) from emp group by post;



    #group_concat（分组之后用）
    select post,group_concat(name) from emp group by post;
    select post,group_concat(name,"_SB") from emp group by post;
    select post,group_concat(name,": ",salary) from emp group by post;
    select post,group_concat(salary) from emp group by post;

    # 补充concat（不分组时用）
    select name as 姓名,salary as 薪资 from emp;

    select concat("NAME: ",name) as 姓名,concat("SAL: ",salary) as 薪资 from emp;

    # 补充as语法
    mysql> select emp.id,emp.name from emp as t1; # 报错
    mysql> select t1.id,t1.name from emp as t1;

3、四则运算

select name,salary*12 as annual_salary from emp;

4、having过滤

having的语法格式与where一模一样，只不过having是在分组之后进行的进一步过滤
    即where不能用聚合函数，而having是可以用聚合函数，这也是他们俩最大的区别

    1、统计各部门年龄在30岁以上的员工平均工资，并且保留平均工资大于10000的部门
    select post,avg(salary) from emp
            where age >= 30
            group by post
            having avg(salary) > 10000;

    #强调：having必须在group by后面使用
    select * from emp
            having avg(salary) > 10000;

5、distinct去重

select distinct post,avg(salary) from emp
            where age >= 30
            group by post
            having avg(salary) > 10000;

6、order by 排序

select * from emp order by salary asc; #默认升序排
select * from emp order by salary desc; #降序排

select * from emp order by age desc; #降序排

select * from emp order by age desc,salary asc; #先按照age降序排，再按照薪资升序排



# 统计各部门年龄在10岁以上的员工平均工资，并且保留平均工资大于1000的部门，
然后对平均工资进行排序

select post,avg(salary) from emp
    where age > 10
    group by post
    having avg(salary) > 1000
    order by avg(salary)
    ;

7、limit限制显示条数

select * from emp limit 3;

select * from emp order by salary desc limit 1;



# 分页显示
select * from emp limit 0,5;
select * from emp limit 5,5;

8、正则表达式

select * from emp where name regexp '^jin.*(n|g)$';