谁能帮我解释一下这段sql语句?
SELECT Orders_D.ID,
qty = sum(mo.prod_qty - mo.defect_qty),
ship_qty = sum(mo.out_qty),
ship_date = max(mo.ship_date)
FROM Orders,
Orders_D,
MO
WHERE ( Orders_D.Order_ID = Orders.ID ) and
( MO.Ord_DID = Orders_D.ID ) and
( ( Orders_D.Status = 0 ) AND
( Orders.Cmp = 0 ) )
GROUP BY Orders_D.ID