What is the average difference in the y coordinate of 2 object samples with the relation "parked on" in image no.1?
relation "parked on" refers to PRED_CLASS = 'parked on'; image no.1 refers to IMG_ID = 1; average difference in the y coordinate = divide(sum(Y), count(PRED_CLASS)) where OBJ1_SAMPLE_ID ! = OBJ2_SAMPLE_ID
SELECT CAST(SUM(T3.Y) AS REAL) / COUNT(CASE WHEN T1.PRED_CLASS = 'parked on' THEN 1 ELSE NULL END) FROM PRED_CLASSES AS T1 INNER JOIN IMG_REL AS T2 ON T1.PRED_CLASS_ID = T2.PRED_CLASS_ID INNER JOIN IMG_OBJ AS T3 ON T2.OBJ1_SAMPLE_ID = T3.OBJ_CLASS_ID WHERE T2.IMG_ID = 1 AND T2.OBJ1_SAMPLE_ID != T2.OBJ2_SAMPLE_ID
database name:db_id image_and_language
ATT_CLASSES table ATT_CLASSES Cols: ATTRIBUTE CLASS ID dtype integer, ATTRIBUTE CLASS dtype text, 
OBJ_CLASSES table OBJ_CLASSES Cols: OBJECT CLASS ID dtype integer, OBJECT CLASS dtype text, 
IMG_OBJ table IMG_OBJ Cols: IMAGE ID dtype integer, OBJECT SAMPLE ID dtype integer, OBJECT CLASS ID dtype integer, X dtype integer, Y dtype integer, W dtype integer, H dtype integer, 
IMG_OBJ_ATT table IMG_OBJ_ATT Cols: IMAGE ID dtype integer, ATTRIBUTE CLASS ID dtype integer, OBJECT SAMPLE ID dtype integer, 
PRED_CLASSES table PRED_CLASSES Cols: PREDICTION CLASS ID dtype integer, PREDICTION CLASS dtype text, 
IMG_REL table IMG_REL Cols: IMAGE ID dtype integer, PREDICTION CLASS ID dtype integer, OBJECT1 SAMPLE ID dtype integer, OBJECT2 SAMPLE ID dtype integer, 
