SQL Magic

schema.sql

CREATE TABLE IF NOT EXISTS `clicks` (
  `id` int primary key not null auto_increment,
  `login` varchar(20) NOT NULL,
  `button` varchar(20) NOT NULL,
  `dt` datetime not null
) DEFAULT CHARSET=utf8;

INSERT INTO `clicks` (`login`, `button`, `dt`) VALUES
  ('Alice', 'blue', NOW()),
  ('Alice', 'red', NOW() - INTERVAL 1 DAY),
  ('Alice', 'green', NOW() - INTERVAL 3 DAY),
  ('Bob', 'red', NOW() - INTERVAL 5 minute),
  ('Bob', 'green', NOW() - INTERVAL 7 hour),
  ('Bob', 'blue', NOW() + INTERVAL 1 day),
  ('Eve', 'red', NOW() - INTERVAL 5 second),
  ('Eve', 'green', NOW() - INTERVAL 2 hour),
  ('Eve', 'blue', NOW() + INTERVAL 7 hour);

test.sql

SELECT login, button, dt FROM clicks WHERE id IN (SELECT id FROM (SELECT id, max(dt) FROM clicks GROUP BY login) t);