[SQL]Remove duplicates

This will also take care of duplicates (return one row for each user_id):

SELECT * FROM (
  SELECT u.*, FIRST_VALUE(u.rowid) OVER(PARTITION BY u.user_id ORDER BY u.date DESC) AS last_rowid
  FROM users u
) u2
WHERE u2.rowid = u2.last_rowid

Ref:
http://stackoverflow.com/questions/121387/fetch-the-row-which-has-the-max-value-for-a-column