GROUP_BITMAP_STATE Function

Description

The GROUP_BITMAP_STATE function builds a BITMAP type result based on the input expression (expr). This function is typically used for grouping operations on integer type data and converting the unique values of each group into a bitmap array.

Parameter Description

• expr: The integer type expression to be processed.

Return Type

• Returns a BITMAP type result.

Usage Examples

Example 1: Build Bitmap by group and view elements

SELECT c, bitmap_to_array(group_bitmap_state(v)) AS bitmap_array FROM VALUES ('a', 1), ('a', 2), ('a', 2), ('b', 3) AS v(c, v) GROUP BY c; +----+--------------+ | c | bitmap_array | +----+--------------+ | a | [1,2] | | b | [3] | +----+--------------+

In this example, group a contains two unique values 1 and 2, and group b contains only the unique value 3.

Example 2: Two-stage aggregation with group_bitmap_merge

First use group_bitmap_state to generate intermediate state by group, then use group_bitmap_merge to merge all groups and obtain the global cardinality:

SELECT group_bitmap_merge(state) AS total FROM ( SELECT c, group_bitmap_state(v) AS state FROM VALUES ('a', 1), ('a', 2), ('b', 2), ('b', 3) AS t(c, v) GROUP BY c ); +-------+ | total | +-------+ | 3 | +-------+