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bitmap_union_count

Description

Returns the union of a set of bitmap values and returns the cardinality of the union.

Syntax

BIGINT bitmap_union_count(BITMAP value)

Parameters

value: a set of bitmap values. The supported data type is BITMAP.

Return value

Returns a value of the BIGINT type.

Examples

Calculate the unique views (UVs) of a web page. If user_id is of the INT type, the latter two queries are equivalent.

mysql> select * from test
+---------+---------+
| page_id | user_id |
+---------+---------+
|       1 |       1 |
|       1 |       2 |
|       2 |       1 |
+---------+---------+

mysql> select page_id,count(distinct user_id) from test group by page_id;
+---------+-------------------------+
| page_id | count(DISTINCT user_id) |
+---------+-------------------------+
|       1 |                       2 |
|       2 |                       1 |
+---------+-------------------------+

mysql> select page_id,bitmap_union_count(to_bitmap(user_id)) from test group by page_id;
+---------+----------------------------------------+
| page_id | bitmap_union_count(to_bitmap(user_id)) |
+---------+----------------------------------------+
|       1 |                                      2 |
|       2 |                                      1 |
+---------+----------------------------------------+