bitmap_union_count
Description
Returns the union of a set of bitmap values and returns the cardinality of the union. This function is supported from v2.3.
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 |
+---------+----------------------------------------+