Question

I have a sample database like this, in which, id is always unique, but the user_id is not unique.

id,user_id,message,msg_datetime
111,u1, msg from u1,time present here
112,u2, msg from u2,time present here
113,u3, msg from u3,time present here
114,u2, msg from u2,time present here
115,u7, msg from u7,time present here
116,u2, msg from u2,time present here
117,u1, msg from u1,time present here
118,u5, msg from u5,time present here

so i want to grab only those unique users who have messaged and order them in DESC by msg_datetime.

This is the query i have.
select id,DISTINCT user_id,msg_datetime ORDER BY msg_datetime DESC but i am getting an error as:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DISTINCT. any help here? what is the correct syntax for what i am trying to achieve?

I want to show only one entry for each user, it does not matter which ID i am showing but only 1 per user.

Answer 1

If you don’t care which record with the same user_id query should return, then

SELECT id,user_id,msg_datetime FROM table_1 GROUP BY user_id ORDER BY msg_datetime DESC

If you want to display, for instance, the last record for each user, you need

SELECT a.user_id, a.last_time, b.id 
FROM
(SELECT user_id, MAX(msg_datetime) as last_time 
 FROM table1)a
INNER JOIN table1 b ON (b.user_id = a.user_id AND b.msg_datetime = a.last_time)

ORDER BY a.last_time;