BITMAP

description

Syntax

TO_BITMAP(expr) : 将TINYINT,SMALLINT和INT类型的列转为Bitmap

BITMAP_UNION(expr) : 计算两个Bitmap的并集，返回值是序列化后的Bitmap值

BITMAP_COUNT(expr) : 计算Bitmap中不同值的个数

BITMAP_UNION_INT(expr) : 计算TINYINT,SMALLINT和INT类型的列中不同值的个数，返回值和 COUNT(DISTINCT expr)相同

注意：

  1. 1. TO_BITMAP 函数输入的类型必须是TINYINT,SMALLINT,INT
  2. 2. BITMAP_UNION函数的参数目前仅支持： 
  3.     - 聚合模型中聚合类型为BITMAP_UNION的列
  4.     - TO_BITMAP 函数

example

  1. CREATE TABLE `bitmap_udaf` (
  2.   `id` int(11) NULL COMMENT "",
  3.   `id2` int(11)
  4. ) ENGINE=OLAP
  5. DUPLICATE KEY(`id`)
  6. DISTRIBUTED BY HASH(`id`) BUCKETS 10;
  9. mysql> select bitmap_count(bitmap_union(to_bitmap(id2))) from bitmap_udaf;
  10. +----------------------------------------------+
  11. | bitmap_count(bitmap_union(to_bitmap(`id2`))) |
  12. +----------------------------------------------+
  13. |                                            6 |
  14. +----------------------------------------------+
  16. mysql> select bitmap_union_int (id2) from bitmap_udaf;
  17. +-------------------------+
  18. | bitmap_union_int(`id2`) |
  19. +-------------------------+
  20. |                       6 |
  21. +-------------------------+
  25. CREATE TABLE `bitmap_test` (
  26.   `id` int(11) NULL COMMENT "",
  27.   `id2` varchar(0) bitmap_union NULL  // 注意： bitmap_union的varchar长度需要指定为0
  28. ) ENGINE=OLAP
  29. AGGREGATE KEY(`id`)
  30. DISTRIBUTED BY HASH(`id`) BUCKETS 10;
  33. mysql> select bitmap_count(bitmap_union(id2)) from bitmap_test;
  34. +-----------------------------------+
  35. | bitmap_count(bitmap_union(`id2`)) |
  36. +-----------------------------------+
  37. |                                 8 |
  38. +-----------------------------------+

keyword

BITMAP,BITMAP_COUNT,BITMAP_UNION,BITMAP_UNION_INT,TO_BITMAP