List the ID of all images with objects that have multiple relations.
ID of all images refer to IMG_ID; if two objects (OBJ1_SAMPLE_ID,
OBJ2_SAMPLE_ID) has
multiple PRED_CLASS_ID, it
means these two objects
have multiple relations;
SELECT IMG_ID FROM IMG_REL GROUP BY PRED_CLASS_ID HAVING COUNT(DISTINCT OBJ1_SAMPLE_ID) != 0 AND COUNT(DISTINCT OBJ2_SAMPLE_ID) != 0