记录相关操作之单表查询之分组查询-练习

一. 准备表

# 提示: 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(个别比较老的windos电脑可能会出现这样的问题)

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),
  office int, #一个部门一个屋子
  depart_id int
);

#插入记录
#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
('tom','male',78,'20150302','teacher',1000000.31,401,1),
('kevin','male',81,'20130305','teacher',8300,401,1),
('tony','male',73,'20140701','teacher',3500,401,1),
('owen','male',28,'20121101','teacher',2100,401,1),
('jack','female',18,'20110211','teacher',9000,401,1),
('jenny','male',18,'19000301','teacher',30000,401,1),
('sank','male',48,'20101111','teacher',10000,401,1),
('哈哈','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('呵呵','female',38,'20101101','sale',2000.35,402,2),
('西西','female',18,'20110312','sale',1000.37,402,2),
('乐乐','female',18,'20160513','sale',3000.29,402,2),
('拉拉','female',28,'20170127','sale',4000.33,402,2),
('僧龙','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);

二. 练习题

# 1. 查询岗位名以及岗位包含的所有员工名字
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
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
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
select post,avg(salary) 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) from emp
    group by post;

# 6. 查询岗位名以及各岗位的最低薪资
select post,min(salary) 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) from emp
    group by