versioned_docs/version-2.1/sql-manual/sql-functions/aggregate-functions/bitmap-union.md

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

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## BITMAP_UNION

### description

### example

#### Create table

The aggregation model needs to be used when creating the table. The data type is bitmap and the aggregation function is bitmap_union.
```
CREATE TABLE `pv_bitmap` (
  `dt` int (11) NULL COMMENT" ",
  `page` varchar (10) NULL COMMENT" ",
  `user_id` bitmap BITMAP_UNION NULL COMMENT" "
) ENGINE = OLAP
AGGREGATE KEY (`dt`,` page`)
COMMENT "OLAP"
DISTRIBUTED BY HASH (`dt`) BUCKETS 2;
```

Note: When the amount of data is large, it is best to create a corresponding rollup table for high-frequency bitmap_union queries

```
ALTER TABLE pv_bitmap ADD ROLLUP pv (page, user_id);
```

#### Data Load

`TO_BITMAP (expr)`: Convert 0 ~ 18446744073709551615 unsigned bigint to bitmap

`BITMAP_EMPTY ()`: Generate empty bitmap columns, used for insert or import to fill the default value

`BITMAP_HASH (expr)` or `BITMAP_HASH64 (expr)`: Convert any type of column to a bitmap by hashing

##### Stream Load

```
cat data | curl --location-trusted -u user: passwd -T--H "columns: dt, page, user_id, user_id = to_bitmap (user_id)" http: // host: 8410 / api / test / testDb / _stream_load
```

```
cat data | curl --location-trusted -u user: passwd -T--H "columns: dt, page, user_id, user_id = bitmap_hash (user_id)" http: // host: 8410 / api / test / testDb / _stream_load
```

```
cat data | curl --location-trusted -u user: passwd -T--H "columns: dt, page, user_id, user_id = bitmap_empty ()" http: // host: 8410 / api / test / testDb / _stream_load
```

##### Insert Into

id2's column type is bitmap
```
insert into bitmap_table1 select id, id2 from bitmap_table2;
```

id2's column type is bitmap
```
INSERT INTO bitmap_table1 (id, id2) VALUES (1001, to_bitmap (1000)), (1001, to_bitmap (2000));
```

id2's column type is bitmap
```
insert into bitmap_table1 select id, bitmap_union (id2) from bitmap_table2 group by id;
```

id2's column type is int
```
insert into bitmap_table1 select id, to_bitmap (id2) from table;
```

id2's column type is String
```
insert into bitmap_table1 select id, bitmap_hash (id_string) from table;
```


#### Data Query

##### Syntax


`BITMAP_UNION (expr)`: Calculate the union of two Bitmaps. The return value is the new Bitmap value.

`BITMAP_UNION_COUNT (expr)`: Calculate the cardinality of the union of two Bitmaps, equivalent to BITMAP_COUNT (BITMAP_UNION (expr)). It is recommended to use the BITMAP_UNION_COUNT function first, its performance is better than BITMAP_COUNT (BITMAP_UNION (expr)).

`BITMAP_UNION_INT (expr)`: Count the number of different values ​​in columns of type TINYINT, SMALLINT and INT, return the sum of COUNT (DISTINCT expr) same

`INTERSECT_COUNT (bitmap_column_to_count, filter_column, filter_values ​​...)`: The calculation satisfies
filter_column The cardinality of the intersection of multiple bitmaps of the filter.
bitmap_column_to_count is a column of type bitmap, filter_column is a column of varying dimensions, and filter_values ​​is a list of dimension values.

##### Example

The following SQL uses the pv_bitmap table above as an example:

Calculate the deduplication value for user_id:

```
select bitmap_union_count (user_id) from pv_bitmap;

select bitmap_count (bitmap_union (user_id)) from pv_bitmap;
```

Calculate the deduplication value of id:

```
select bitmap_union_int (id) from pv_bitmap;
```

Calculate the retention of user_id:

```
select intersect_count (user_id, page, 'meituan') as meituan_uv,
intersect_count (user_id, page, 'waimai') as waimai_uv,
intersect_count (user_id, page, 'meituan', 'waimai') as retention // Number of users appearing on both 'meituan' and 'waimai' pages
from pv_bitmap
where page in ('meituan', 'waimai');
```

### keywords

BITMAP, BITMAP_COUNT, BITMAP_EMPTY, BITMAP_UNION, BITMAP_UNION_INT, TO_BITMAP, BITMAP_UNION_COUNT, INTERSECT_COUNT