For those objects that have multiple relations, how many images have a prediction class of "reading"?
prediction class of "reading" refers to PRED_CLASS = 'reading'; if two objects (OBJ1_SAMPLE_ID,
OBJ2_SAMPLE_ID) has
multiple PRED_CLASS_ID, it
means these two objects
have multiple relations;
SELECT COUNT(T1.IMG_ID) FROM IMG_REL AS T1 INNER JOIN PRED_CLASSES AS T2 ON T1.PRED_CLASS_ID = T2.PRED_CLASS_ID WHERE T2.PRED_CLASS = 'reading'