Define the onion's bounding box on image no. 285930.
bounding box refers to (X, Y, W, H); onion refers to OBJ_CLASS = 'onion'; image no.285930 refers to IMG_ID = 285930
SELECT T1.X, T1.Y, T1.W, T1.H FROM IMG_OBJ AS T1 INNER JOIN OBJ_CLASSES AS T2 ON T1.OBJ_CLASS_ID = T2.OBJ_CLASS_ID WHERE T1.IMG_ID = 285930 AND T2.OBJ_CLASS = 'onion'