Checking for an output of 1 from ST_Relate will still indicate that the features are equal, except in the case where both input parameters are empty. A more robust method is to check whether geometries are empty when calling ST_Relate. If both are empty, they may be considered equal. If one is empty and the other is not, then they are not equal. For example, to find all combinations of matching features in TBL1 and TBL2select (TBL1.OBJECTID, TBL2.OBJECTID) from TBL1, TBL2 WHERE ST_Relate(TBL1.SHAPE,TBL2.SHAPE, 'T*F**FFF*') = 1 OR ( ST_IsEmpty(TBL1.SHAPE) = 0 AND ST_IsEmpty(TBL2.SHAPE) = 0 );