---
{
    "title": "bitmap_intersect",
    "language": "zh-CN"
}
---

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# bitmap_intersect
## description

聚合函数，用于计算分组后的 bitmap 交集。常见使用场景如：计算用户留存率。

### Syntax

`BITMAP BITMAP_INTERSECT(BITMAP value)`

输入一组 bitmap 值，求这一组 bitmap 值的交集，并返回。

## example

表结构

```
KeysType: AGG_KEY
Columns: tag varchar, date datetime, user_id bitmap bitmap_union

```

```
求今天和昨天不同 tag 下的用户留存
mysql> select tag, bitmap_intersect(user_id) from (select tag, date, bitmap_union(user_id) user_id from table where date in ('2020-05-18', '2020-05-19') group by tag, date) a group by tag;
```

和 bitmap_to_string 函数组合使用可以获取交集的具体数据

```
求今天和昨天不同 tag 下留存的用户都是哪些
mysql> select tag, bitmap_to_string(bitmap_intersect(user_id)) from (select tag, date, bitmap_union(user_id) user_id from table where date in ('2020-05-18', '2020-05-19') group by tag, date) a group by tag;
```

## keyword

    BITMAP_INTERSECT, BITMAP