单表查询

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
(‘alice‘,‘female‘,18,‘20170301‘,‘teacher‘,7300.33,401,1), #以下是教学部
(‘nico‘,‘female‘,78,‘20150302‘,‘teacher‘,1000000.31,401,1),
(‘anna‘,‘female‘,81,‘20130305‘,‘teacher‘,8300,401,1),
(‘jack‘,‘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;  # 查年薪（内存中的虚拟表）annual_salary为表名（不加as也可以）
    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;
   
   SELECT CONCAT(‘姓名: ‘,name,‘  年薪: ‘, salary*12)  AS Annual_salary,post
   FROM employee;     # 再加一个职位字段

   SELECT CONCAT(‘姓名: ‘,name,‘  性别: ‘, sex） AS Info, CONCAT("薪资": ‘,salary*12 ) AS Annual_salary  FROM employee;

   CONCAT_WS() 第一个参数为分隔符
   SELECT CONCAT_WS(‘:‘,name,sex,age)  AS Annual_salary FROM employee;   #显示“姓名：性别：年龄”

   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;

select distinct post from employee;   # 查询职位，去重

# 四则运算
 select name,salary*12 as annual_salary from employee   # 查年薪（内存中的虚拟表）annual_salary为表名（不加as也可以）


#自己规定格式
select concat() from employee;

#1:单条件查询
    SELECT name FROM employee
        WHERE post=‘sale‘;
        
#2:多条件查询
    SELECT name,post,salary FROM employee
        WHERE post=‘teacher‘ AND salary>10000;     # 找出薪资大于10000的老师

#3:关键字BETWEEN AND  （本质就是大于等于和小于等于）
    SELECT name,salary FROM employee 
        WHERE salary BETWEEN 10000 AND 20000;     # 找出薪资在10000和20000的老师

    SELECT name,salary FROM employee 
        WHERE salary NOT BETWEEN 10000 AND 20000;     # 找出薪资小于10000和大于20000的老师
    
#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,age,salary FROM employee 
        WHERE age=73 OR age=81 OR age=28;   #找出年龄是73或者81或者28的
    
    SELECT name,age,salary FROM employee 
        WHERE age IN (73,28,81) ;    # 上述的简单方法

    SELECT name,age,salary FROM employee 
        WHERE age NOT IN (73,28,81) ;

#6:关键字LIKE模糊查询
    通配符’%’
    SELECT * FROM employee 
            WHERE name LIKE ‘al%‘;    # 名字是al开头，%任意多个字符

    通配符’_’
    SELECT * FROM employee 
            WHERE name LIKE ‘j__‘;   # _ 任意一个字符（可以用多个）

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%‘;