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Version: Stable-3.1

unnest_bitmap

Description

unnest_bitmap is a table function that takes a bitmap and converts elements in that bitmap into multiple rows of a table.

StarRocks' Lateral Join can be used in conjunction with the unnest_bitmap function to implement common column-to-row logic.

This function can be used to replace unnest(bitmap_to_array(bitmap)). It has better performance, takes up less memory resources, and is not limited by the length of the array.

This function is supported from v3.1.

Syntax

unnest_bitmap(bitmap)

Parameters

bitmap: the bitmap you want to convert.

Return value

Returns multiple rows converted from the bitmap. The type of return value is BIGINT.

Examples

c2 is a bitmap column in table t1.

-- Use the bitmap_to_string function to convert values in the c2 column into a string.
mysql> select c1, bitmap_to_string(c2) from t1;
+------+----------------------+
| c1 | bitmap_to_string(c2) |
+------+----------------------+
| 1 | 1,2,3,4,5,6,7,8,9,10 |
+------+----------------------+

-- Use the unnest_bitmap function to expand the bitmap column into multiple rows.
mysql> select c1, unnest_bitmap from t1, unnest_bitmap(c2);
+------+---------------+
| c1 | unnest_bitmap |
+------+---------------+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 1 | 5 |
| 1 | 6 |
| 1 | 7 |
| 1 | 8 |
| 1 | 9 |
| 1 | 10 |
+------+---------------+