# PFMERGE

> Merge multiple HyperLogLogs.

Use `PFMERGE` to merge several HyperLogLogs into a single one.

The destination ends up representing the union of the source structures and of whatever it already held, so merging the same sources again changes nothing and new data can be folded in as it arrives. The destination is created if it does not exist.

Because the union is computed register by register and loses no accuracy compared with counting the raw data, rolling hourly keys into a daily key, or daily keys into a monthly one, gives the same estimate as if every element had been added to that key directly. That makes `PFMERGE` the building block for time-based rollups of unique counts.

## Syntax

```redis
PFMERGE <destkey> [<sourcekey> [<sourcekey> ...]]
```

## Arguments

| Argument | Required | Repeatable | Description |
| --- | --- | --- | --- |
| `<destkey>` | Yes | No | Redis key used as destkey. |
| `<sourcekey>` | No | Yes | Redis key used as sourcekey. |

## Response

The reply reports the result of the operation. Error replies have the same shape in RESP2 and RESP3 and are surfaced as exceptions by the SDKs below.

| Protocol | Reply |
| --- | --- |
| RESP2 | Simple string `OK` |
| RESP3 | Simple string `OK` |

<Note>
  Client libraries often decode bulk strings, maps, sets, and numeric strings into language-native values. The table describes the Redis wire reply.
</Note>

## Examples

TCP examples use the TLS `REDIS_URL` from the Upstash console. REST examples use `UPSTASH_REDIS_REST_URL` and `UPSTASH_REDIS_REST_TOKEN`.

<AccordionGroup>

<Accordion title="Redis CLI" icon="terminal">

```bash
PFMERGE destination-key source-key
```

</Accordion>

<Accordion title="@upstash/redis" icon="node-js" iconType="brands">

```ts
import { Redis } from "@upstash/redis";

const redis = Redis.fromEnv();
const result = await redis.pfmerge("destination-key", "source-key");
console.log(result);
```

</Accordion>

<Accordion title="upstash_redis" icon="python" iconType="brands">

```python
from upstash_redis import Redis

redis = Redis.from_env()
result = redis.pfmerge("destination-key", "source-key")
print(result)
```

</Accordion>

<Accordion title="ioredis" icon="node-js" iconType="brands">

```ts
import Redis from "ioredis";

const redis = new Redis(process.env.REDIS_URL!);
const result = await redis.pfmerge("destination-key", "source-key");
console.log(result);
```

</Accordion>

<Accordion title="node-redis" icon="node-js" iconType="brands">

```ts
import { createClient } from "redis";

const client = await createClient({ url: process.env.REDIS_URL })
  .on("error", console.error)
  .connect();
const result = await client.pfMerge("destination-key", "source-key");
console.log(result);
```

</Accordion>

<Accordion title="redis-py" icon="python" iconType="brands">

```python
import os
import redis

client = redis.from_url(os.environ["REDIS_URL"])
result = client.pfmerge("destination-key", "source-key")
print(result)
```

</Accordion>

<Accordion title="go-redis" icon="golang" iconType="brands">

```go
package main

import (
    "context"
    "fmt"
    "os"

    "github.com/redis/go-redis/v9"
)

func main() {
    opts, err := redis.ParseURL(os.Getenv("REDIS_URL"))
    if err != nil {
        panic(err)
    }
    client := redis.NewClient(opts)
    result, err := client.PFMerge(context.Background(), "my-key").Result()
    if err != nil {
        panic(err)
    }
    fmt.Println(result)
}
```

</Accordion>

<Accordion title="jedis" icon="java" iconType="brands">

```java
import java.net.URI;

import redis.clients.jedis.Jedis;

try (Jedis jedis = new Jedis(new URI(System.getenv("REDIS_URL")))) {
  Object result = jedis.pfmerge("my-key");
  System.out.println(result);
}
```

</Accordion>

<Accordion title="redis-rs" icon="rust" iconType="brands">

```rust
use redis::TypedCommands;

fn main() -> redis::RedisResult<()> {
    let url = std::env::var("REDIS_URL").expect("REDIS_URL is not set");
    let client = redis::Client::open(url)?;
    let mut connection = client.get_connection()?;

    let result = connection.pfmerge("destination-key", &["source-key"])?;
    println!("{result:?}");
    Ok(())
}
```

</Accordion>

</AccordionGroup>