Question

In SQL Server 2008 I have two tables. One table for users:

id_user - integer, primary key 
id_group - integer 
username - varchar 
phone - varchar 
id_coordinating - int

Sample data:

1, 1, admin,       0230029921, NULL 
2, 2, supervisor1, 0230029933, NULL
3, 2, supervisor2, 0321211233, NULL 
4, 3, user1,       0321222323, 2 
5, 3, user2,       0323211232, 2 
6, 3, user3,       0324223121, 3

All users in group USERS have one supervisor represented by the id_user

And another table for groups

id_group - integer, primary key 
groupname - varchar 

Sample data:

1, Administrators 
2, Supervisors 
3, Users 

I’m running the the following query:

select  id_user, username,  group.groupname, phone, id_coordinating
from users  
INNER JOIN group ON users.id_group = group.id_group 

and I get the following result:

1 1 admin        Administrators 0230029921 NULL
2 2 supervisor1  Supervisors    0230029933 NULL
3 2 supervisor2  Supervisors    0321211233 NULL 
4 3 user1        Users          0321222323 2
5 3 user2        Users          0323211232 2 
6 3 user3        Users          0324223121 3

I want to replace the id_coordonating with the username and look like this…

1 1 admin        Administrators 0230029921 NULL 
2 2 supervisor1  Supervisors    0230029933 NULL 
3 2 supervisor2  Supervisors    0321211233 NULL 
4 3 user1        Users          0321222323 supervisor1  
5 3 user2        Users          0323211232 supervisor1  
6 3 user3        Users          0324223121 supervisor2 

Thanks,

Answer 1

You can left join back onto your users table for this.

select
  u.id_user, 
  u.username,  
  g.groupname, 
  u.phone,
  u2.username
from users u
join group g
  on u.id_group = g.id_group
left join users u2
  on u.id_coordinating = u2.id_user