---
{
    "title": "bitmap_union",
    "language": "en"
}
---

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# bitmap_union
## description

Aggregate function, used to calculate the grouped bitmap union. Common usage scenarios such as: calculating PV, UV.

### Syntax

`BITMAP BITMAP_UNION(BITMAP value)`

Enter a set of bitmap values, find the union of this set of bitmap values, and return.

## example

```
mysql> select page_id, bitmap_union(user_id) from table group by page_id;
```

Combined with the bitmap_count function, the PV data of the web page can be obtained

```
mysql> select page_id, bitmap_count(bitmap_union(user_id)) from table group by page_id;
```

When the user_id field is int, the above query semantics is equivalent to

```
mysql> select page_id, count(distinct user_id) from table group by page_id;
```

## keyword

    BITMAP_UNION, BITMAP