SUNIONCARD - Upstash Documentation

Use SUNIONCARD to count the distinct members that appear in at least one of the given sets. It returns only the count; use 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#

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.

Redis CLI

> 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:

SUNIONCARD 2 set1 set2 APPROXSUNIONCARD 2 set1 set2 APPROX LIMIT 3

@upstash/redis

Note

This command is not supported yet in @upstash/redis.

upstash_redis

Note

This command is not supported yet in upstash_redis.

ioredis

import Redis from "ioredis";const redis = new Redis(process.env.REDIS_URL!);const result = await redis.sunioncard(2, "set1", "set2");console.log(result);

node-redis

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);

redis-py

import osimport redisclient = redis.from_url(os.environ["REDIS_URL"])result = client.sunioncard(2, ["set1", "set2"])print(result)

go-redis

package mainimport (    "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)}

jedis

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);}

redis-rs

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(())}