Support bitmap_intersect

[EmmyMiao87]

Support aggregate function Bitmap Intersect, it is mainly used to take intersection of grouped data.
The function 'bitmap_intersect(expr)' calculates the intersection of bitmap columns and returns a bitmap object.
The defination is following:
FunctionName: bitmap_intersect,
InputType: bitmap,
OutputType: bitmap

The scenario is as follows:
Query which users satisfy the three tags a, b, and c at the same time.

select bitmap_to_string(bitmap_intersect(user_id)) from
(
select bitmap_union(user_id) user_id from bitmap_intersect_test
where tag in ('a', 'b', 'c')
group by tag
) a

Closed#3552.

Change-Id: I0d50c9bb6827f7319c4d854f621412343a3ece24

[EmmyMiao87]

I will add sql-reference later.

[kangkaisen]

Would better add a UNLIKELY macros.

[imay]

why initial result bitmap as null? it seems that it will return empty bitmap when result bitmap is null

[EmmyMiao87]

The initial result bitmap must be null. Otherwise, the intersection between dst and src will be empty.

[kangkaisen]

@EmmyMiao87 Hi.
当前对于 bitmap_intersect null的处理是不合理的。

按照SQL标准，sum(null), min(null), max(null)结果为 null. count(null)为0.

所以 对于 bitmap_intersect，bitmap_union 返回bitmap的函数，输入全是null时，应该返回null,
对于 bitmap_intersect_count, bitmap_union_count 等返回count值的函数， 输入全是null时，应该返回0.

在之前最开始的时候，我认为所有hll,bitmap的函数都不需要返回null，对于输入是null，我们返回empty bitmap 或者empty hll 即可。（it's my fault...）

所以目前bitmap_init, bitmap_serialize, bitmap_finalize的实现都是not nullable的。
所以你这个PR，你应该实现新的函数 nullable_bitmap_int, nullable_bitmap_serialize。nullable_bitmap_serialize 中src是null, 应该返回null，而不是空的empty.

[imay]

LGTM

[kangkaisen]

+1, LGTM

[kangpinghuang]

LGTM, +1

[kangpinghuang]

LGTM