MySQL query to fill in missing dates with a sparse result set

mysql-sparse-fill-in.sql

/* For a query of results in the last 31 days */

SELECT recent_dates.`date`,
      IFNULL(sparse_results.`count`, 0) AS `count`
FROM
  (SELECT SUBDATE(CURDATE(), number_table.delta) AS `date`
  FROM
    (SELECT 0 delta
      UNION SELECT 1
      UNION SELECT 2
      UNION SELECT 3
      UNION SELECT 4
      UNION SELECT 5
      UNION SELECT 6
      UNION SELECT 7
      UNION SELECT 8
      UNION SELECT 9
      UNION SELECT 10
      UNION SELECT 11
      UNION SELECT 12
      UNION SELECT 13
      UNION SELECT 14
      UNION SELECT 15
      UNION SELECT 16
      UNION SELECT 17
      UNION SELECT 18
      UNION SELECT 19
      UNION SELECT 20
      UNION SELECT 21
      UNION SELECT 22
      UNION SELECT 23
      UNION SELECT 24
      UNION SELECT 25
      UNION SELECT 26
      UNION SELECT 27
      UNION SELECT 28
      UNION SELECT 29
      UNION SELECT 30
      UNION SELECT 31) AS number_table) AS recent_dates
LEFT JOIN
  (SELECT FROM_UNIXTIME(activity_completed, '%Y-%m-%d') AS `date`,
          COUNT(id) AS `count`
  FROM mytable
  GROUP BY `date`
  ORDER BY `date` DESC
  LIMIT 33) AS sparse_results ON recent_dates.`date` = sparse_results.`date`
ORDER BY recent_dates.`date` ASC