CREATE TABLE ml_latest
(
   lnid     SMALLINT UNSIGNED NOT NULL,
   dmid     TINYINT UNSIGNED NOT NULL,
   itid     SMALLINT UNSIGNED NOT NULL,
   PRIMARY KEY (lnid, dmid, itid),
   txtid    INT UNSIGNED NOT NULL,
   chgtime  DATETIME NOT NULL,
   staleness  TINYINT UNSIGNED DEFAULT 0 NOT NULL, # better than ENUM('0','1','2');
   INDEX (lnid, staleness),
   INDEX (dmid, itid),
   INDEX (lnid, dmid, chgtime),
   INDEX (chgtime)
)