mysql 多表join

两个表可以简单地写为

select a.,b. from a left join b on a.id =b.id;
三个以上
select a.,b. from a left join b on a.id=b.id left join c on a.id=b.id where

具体的例子

select id,people_num,count(proj_name) as count_project from employee join department on employee.in_dpt = department.dpt_name join project on project.of_dpt=employee.in_dpt order by id;