Você pode tentar desta forma.
SELECT t.* FROM mytable t
JOIN
( SELECT item, MIN(value) minVal
FROM mytable GROUP BY item
) t2
ON t.value = t2.minVal AND t.item = t2.item;
SELECT t.* FROM mytable t
JOIN
( SELECT item, MIN(value) minVal
FROM mytable GROUP BY item
) t2
ON t.value = t2.minVal AND t.item = t2.item;