# SUNIONCARD

> Get set union cardinality.

Use `SUNIONCARD` to count the distinct members that appear in at least one of the given sets. It returns only the count; use [`SUNION`](/redis/commands/set/sunion) to retrieve the members.

Members shared by multiple sets count once. Keys that do not exist count as empty sets, and the command returns `0` if all keys are missing. It does not modify the source sets or store the union.

`LIMIT` stops counting once that many distinct members have been found and returns the limit. Omitting `LIMIT` or using `LIMIT 0` returns the full count.

## Syntax

```redis
SUNIONCARD <numkeys> <key> [<key> ...] [APPROX] [LIMIT <limit>]
```

## Arguments

| Argument | Required | Repeatable | Description |
| --- | --- | --- | --- |
| `<numkeys>` | Yes | No | Positive integer specifying how many key arguments follow. |
| `<key>` | Yes | Yes | Set key to include in the union. |
| `APPROX` | No | No | Estimate the union cardinality using HyperLogLog instead of counting exactly. |
| `LIMIT <limit>` | No | No | Non-negative integer that caps the returned count; `0` means no limit. |

## Important points

- `numkeys` must equal the number of key arguments that immediately follow it.
- The count is exact unless `APPROX` is specified.
- `APPROX` uses a temporary HyperLogLog to reduce the memory needed to track distinct members. The inputs are ordinary sets, and the result may differ from the exact cardinality.
- `APPROX` and `LIMIT` can appear in either order after the keys. With both options, counting can stop when the estimate reaches the limit, and the returned value never exceeds that limit.

## Response

The number of distinct members in the union, or an estimate when `APPROX` is specified. A positive `LIMIT` caps the returned value in either mode.

| Protocol | Reply |
| --- | --- |
| RESP2 | Integer |
| RESP3 | Integer |

## Examples

TCP examples use the TLS `REDIS_URL` from the Upstash console. Client examples query `set1` and `set2` from the Redis CLI example.

<AccordionGroup>

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

```redis
> SADD set1 a b c
(integer) 3
> SADD set2 c d e
(integer) 3
> SUNIONCARD 2 set1 set2
(integer) 5
> SUNIONCARD 2 set1 set2 LIMIT 3
(integer) 3
> SUNIONCARD 2 set1 set2 LIMIT 0
(integer) 5
```

The union contains `a`, `b`, `c`, `d`, and `e`. The shared member `c` counts once.

To estimate the count, optionally capped at a limit:

```redis
SUNIONCARD 2 set1 set2 APPROX
SUNIONCARD 2 set1 set2 APPROX LIMIT 3
```

</Accordion>

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

<Note>
  This command is not supported yet in `@upstash/redis`.
</Note>

</Accordion>

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

<Note>
  This command is not supported yet in `upstash_redis`.
</Note>

</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.sunioncard(2, "set1", "set2");
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.sUnionCard(["set1", "set2"]);
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.sunioncard(2, ["set1", "set2"])
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)
    defer client.Close()
    result, err := client.SUnionCard(context.Background(), nil, "set1", "set2").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")))) {
  long result = jedis.sunioncard("set1", "set2");
  System.out.println(result);
}
```

</Accordion>

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

```rust
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 mut command = redis::cmd("SUNIONCARD");
    command.arg(2).arg("set1").arg("set2");
    let result: i64 = command.query(&mut connection)?;
    println!("{result:?}");
    Ok(())
}
```

</Accordion>

</AccordionGroup>