USE prosody;
SET autocommit=0;

DELETE FROM prosody
WHERE (host, user, store, `key`, `value`) NOT IN (
    SELECT t.host, t.user, t.store, t.`key`, t.max_value
    FROM (
        SELECT host, user, store, `key`, MAX(value) AS max_value
        FROM prosody
        GROUP BY host, user, store, `key`
    ) AS t
);

DROP INDEX prosody_index on prosody;
CREATE UNIQUE INDEX prosody_unique_index ON prosody(`host`(20), `user`(20), `store`(20), `key`(20)) USING BTREE;
COMMIT;