1. create a project node to adjust the output column position when a mv is selected in olap scan node
2. pass SlotReference's column info when call Alias's toSlot() method
3. should compare plan's logical properties when compare two plans after rewrite
Result of functions grouping and grouping_id is always not nullable, but outer join will convert the result column to nullable when necessary, which will cause mismatch of column type and column object when executing unctions grouping and grouping_id.
