数据库之表的查询方式

create table emp(
  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),
);


#三个部门：教学，销售，运营
insert into emp(name,sex,age,hire_date,post,salary,office,depart_id) values
(‘jason‘,‘male‘,18,‘20170301‘,‘张江第一帅形象代言‘,7300.33,401,1), #以下是教学部
(‘egon‘,‘male‘,78,‘20150302‘,‘teacher‘,1000000.31,401,1),
(‘kevin‘,‘male‘,81,‘20130305‘,‘teacher‘,8300,401,1),
(‘tank‘,‘male‘,73,‘20140701‘,‘teacher‘,3500,401,1),
(‘owen‘,‘male‘,28,‘20121101‘,‘teacher‘,2100,401,1),
(‘jerry‘,‘female‘,18,‘20110211‘,‘teacher‘,9000,401,1),
(‘nick‘,‘male‘,18,‘19000301‘,‘teacher‘,30000,401,1),
(‘sean‘,‘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)
;

# 1.查询id大于等于3小于等于6的数据
select * from emp where id >= 3 and id <= 6;
select name,salary from emp where id between 3 and 6;  # 查询id(3-6)之间姓名 薪资

# 2.查询薪资是20000或者18000或者17000的数据
select * from emp where salary = 20000 or salary = 18000 or salary = 17000;
select name,id from emp where salary in (20000,18000,17000); 查看薪资在（20000 180000 17000）姓名 ID


# 3.查询员工姓名中包含o字母的员工姓名和薪资

select name,id from emp where name like ‘%o%‘;   # 模糊匹配 匹配出所有含有o字母

# 4.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 emp where name like ‘____‘;
select name,salary,id from emp where  char_length(name) = 4;


# 5.查询id小于3或者大于6的数据
select * from emp where id > 3 or id < 6;
select * from emp where id not between 3 and 6;

# 6.查询薪资不在20000，18000，17000范围的数据
select * from emp where salary not in(20000,18000,17000);

# 7.查询岗位描述为空的员工名与岗位名
select * from emp where post_comment = Null; # 不会报错 但是会匹配不到数据

select * from emp where post_comment is Null; # null 需要用is

select * from emp group by post;
PS:
(1)分组获取的以组为单位    获取的是组内的第一条数据
(2)在MySQL分组之后 只能获取分组后组内的字段信息 无法获取其余字段信息
(3)上述可以通过聚合函数 获取其余字段信息
(4)如果分组之后 依然可以获取到其余字段信息 说明没有设置严格模式
# 严格模式设置
set global sql_mode = "strict_trans_tables,only_full_group_by";
select * from emp group by post; # 报错
select name from emp group by post; # 报错
select post from emp group by post; # 查询成功

# 1.获取每个部门的最高工资
select post,max(salary) from emp group by post;
 
# 每个部门的最低工资
select post,min(salary) from emp group by post;

# 每个部门的平均工资
select post,avg(salary) from emp group by post;

# 每个部门的工资总和
select post,sum(salary) from emp group by post;

#  每个部门的人数
select post,count(id) from emp group by post;
select post,count(salary) from emp group by post;
select post,count(null) from emp group by post; # 无法统计
PS:在统计分组个数的时候 可以将非空字段当做参数传入count 完成计数

# 3.查询分组之后的部门名称和每个部门下所有的姓名
select post,name from emp group by post;  # 报错
select post,group_concat(name) from emp group by post;

# 查询分组之后的部门名称和每个部门下所有的姓名 并将选出的数据名添加_SR
select post,group_concat(name,‘_SR‘) from emp group by post;

# 查询分组之后的部门名称和每个部门下所有的姓名与薪水 并将选出的数据进行拼接
select post,group_concat(name,‘:‘,salary) from emp group by post;

# 查询分组之后的部门名称和每个部门下所有的姓名与薪水 并将选出的数据进行拼接且通过as重命名表名
select concat(‘NAME‘,‘:‘,name) as 姓名,concat(‘SLA‘,‘:‘,salary) as 薪水 from emp where id between 3 and 6;

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 from emp where age > 30 group by post having avg(salary) >10000;
PS:
(1):having只能用在分组后面
(2):having不能单独使用
select post from emp where age > 30 having avg(salary) >10000;  # 报错 
select post from emp having avg(salary) >10000;                    # 报错