Question

This is my SQL:

"SELECT users.username, users.id_user, friends.name, friends.meet_date 
 FROM users INNER JOIN friends ON (users.id_user = friends.id_user) 
 GROUP BY username ORDER BY username";

This is the output on my webpage:

Username    Friend's Name    Meeting Date
George      Nicolas          2010
Man         Anatol           2008

For now, it selects just the first rows from database for each user.

Each table has an auto_increment, id_user for the first table and id_friend for the second one.

I would like it to show that friend which were meet last by each user.

I’ve tried to add an order by "meet_date DESC" but it doesn’t work.

How could I achieve my wish?

Answer 1

The easy way is a subquery:

 SELECT 
   users.username, 
   users.id_user, 
   ( select friends.name  
     from friends 
     where (users.id_user = friends.id_user) 
     ORDER BY friends.meet_date desc
     LIMIT 1 ) as friend_name,       
   ( select friends.meet_date
     from friends 
     where (users.id_user = friends.id_user) 
     ORDER BY friends.meet_date desc
     LIMIT 1 ) as friend_meet_date
 FROM users 
 ;

* Testing *

create table users (username varchar(50), id_user int);
create table friends ( name varchar(50), id_user int, meet_date int);

insert into users values ( 'a', 1),('b',2);
insert into friends values ('c', 1, 0), ('d',1,1);

Results:

| USERNAME | ID_USER | FRIEND_NAME | FRIEND_MEET_DATE |
-------------------------------------------------------
|        a |       1 |           d |                1 |
|        b |       2 |      (null) |           (null) |

Try it at sql fiddle.

Notice thant a correlated subquery is not an elegant approach, is the easy approach.