Question

I’ve got the following problem:
I have two tables: (simplified)

+--------+    +-----------+
| User   |    | Role      |
+--------+    +-----------+
| ID<PK> |    | ID <PK>   |
+--------+    | Name      |
              +-----------+

and M:N relationship between them

+-------------+   
| User_Role   |   
+-------------+
| User<FK>    |
| Role<FK>    |
+-------------+

I need to create a view, which selects me: User, and in one column, all of his Roles (this is done by group_concat).

I’ve tried following:

SELECT u.*, group_concat(r.Name separator ',') as Roles FROM 
  User u
  LEFT JOIN User_Role ur ON ur.User=u.ID
  LEFT JOIN Role r ON ur.Role=r.ID
 GROUP BY u.ID;

However, this works for an user with some defined roles. Users without role aren’t returned. How can I modify the statement, to return me User with empty string in Roles column when User doesn’t have any Role?

Explanation: I’m passing the SQL data directly to a grid, which then formats itself, and it is easier for me to create slow and complicated view, than to format it in my code.

I’m using MySQL

Answer 1

I have try your SQL and have no pb to run it , all row are returned even user without role, the only thing that you have null into the roles column, to avoid that use COALESCE function to get an empty string when the field will be NULL.

SELECT u.*, group_concat(COALESCE(r.Name, "") separator ',') as Roles FROM 
  User u
  LEFT JOIN User_Role ur ON ur.User=u.ID
  LEFT JOIN Role r ON ur.Role=r.ID
 GROUP BY u.ID;