9 having 过滤条件 / order by 排序字段 / limit

select post,group_concat(name),count(id) from employee group by post 
having count(id)<2;

select post, avg(salary) from employee group up post 
having avg(salary)>10000 and avg(salary)<20000;

order by

select * from employee order by age asc; #默认升序

select * from employee order by age desc; 

select * from employee order by age asc,id desc; 

select post, count(id) as emp_count from employee
where salary>500
group by post
having count(id)>1
order by count(id) desc;

 

 

limit

select * from employee limit 3;

select * from employee order by salary desc limit 1;

select * from employee limit 0,5;
select * from employee limit 5,5;
select * from employee limit 10,5;
select * from employee limit 15,5;

 

#总结：

语法顺序

执行顺序