CBO always chooses an index with "maximum" index pushdown

With a query containing GROUP BY and/or aggregation, when there are multiple indexes available that can do group aggregates pushdown, the cost-based optimizer (CBO) currently always chooses the index with the "maximum" pushdown, e.g., it'll choose an index with full group/aggregate pushdown over an index with partial group/aggregate pushdown, regardless of cost. This can result in an inefficient index being chosen.