[Optimizer] Add a new rule to prune no-used columns to speed up query performance for aggregate-union-aggregate pattern

[LiShuMing]

Enhancement

For the query below, we can do som optimizations if:

• parent's aggs can be roll-up and rollup from union's aggs;
• parent's gb-keys comes from union's gb-keys.

before

select col1, sum(col3) from --  parent
(

	select col1, col2, sum(col3) as col3 from t1 group by col1, col2 -- child
	union all
	select col1, col2, sum(col3) as col3 from t1 group by col1, col2
) t
group by col1;

after:

select col1, sum(col3) from
(

	select col1, sum(col3) as col3 from t1 group by col1
	union all
	select col1, sum(col3) as col3 from t1 group by col1
) t
group by col1;

This can prune no-used columns to speed up query performance.