Question

I have a table that stores locations of users. I would like to select the latest location of every user.

What I’ve tried

SELECT lat, lng, address, idUser, timestamp FROM locations ORDER BY timestamp DESC LIMIT 1

SELECT lat, lng, address, idUser, MAX(timestamp) FROM locations

Those two, of course, gave me the last location among all users. The structure of the table is simple:

CREATE TABLE `locations` (
  `idLocation` int(11) NOT NULL auto_increment,
  `idUser` int(11) NOT NULL,
  `address` varchar(255) NOT NULL,
  `lat` float(10,6) NOT NULL,
  `lng` float(10,6) NOT NULL,
  `timestamp` timestamp NOT NULL default CURRENT_TIMESTAMP,
  PRIMARY KEY  (`idLocation`),
  KEY `idUser` (`idUser`)
)

Answer 1

I found the solution in this page, using a self join. Get the latest timestamp for each user and then get the rest of the row by self-joining.

http://www.xaprb.com/blog/2006/12/07/how-to-select-the-firstleastmax-row-per-group-in-sql/

SELECT
l.idUser,
l.lat,
l.lng,
l.timestamp
FROM (
select idUser, max(timestamp) as maxtimestamp
from locations group by idUsuario)
as max inner join locations as l on l.idUsuario = max.idUsuario and l.timestamp = max.maxtimestamp
GROUP BY idUsuario