day47 练习

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