如何连接两个具有一对多关系的表？

Question

I've one user table and another user_project table which contains primary key of user as its foreign key and user can have one or more projects. I need to join these tables to get comma separated project names for particular user.

I've tried something like this -

select group_concat(epi.project_name)
from user u
     inner join employee_projects_info epi on epi.employee_id= u.id
group by epi.project_name

but it is not giving me list of projects user wise.

Answer 1

remove epi.project_name from group by , add epi.employee_id in group by

select epi.employee_id,group_concat(epi.project_name) 
from user u inner join employee_projects_info epi 
on epi.employee_id= u.id 
group by epi.employee_id

Answer 2

make group by id and concat all project name:

 select epi.employee_id, group_concat(epi.project_name)
from user u    inner join employee_projects_info epi on epi.employee_id= u.id
group by epi.employee_id

Answer 3

First, try to get all the users along with their projects. You can get that data by

select u.id,epi.id,epi.project_name
from users u
inner join employee_projects_info epi on epi.employee_id = u.id

To get the comma separated project names for every user, you'll have to use group by in the above query. You can find that query in other people's answers.