When an inner join with a predicate that can be copied is pushed, we will still create the copied criteria. In some situations, this over-constraining is not desirable. We should minimize when this occurs. For example:

select col1 from t1, t2 where t1.col = t2.col and t1.col = 1

should pushdown as:

select col1 from t1, t2 where t1.col = t2.col and t1.col = 1

not:

select col1 from t1, t2 where t1.col = t2.col and t1.col = 1 and t2.col = 1