---
title: "Redis Sets and Sorted Sets"
type: concept
tags: [sets, sorted-sets, leaderboards, set-operations]
updated: 2026-06-25
confidence: high
sources: [raw/web_community-index-html-md-4.md, raw/web_community-index-html-md-6.md]
---
# Redis Sets and Sorted Sets

## Sets

A Redis set is an unordered collection of unique strings (members). Sets efficiently track unique items, represent relations, and perform set operations. Adding, removing, and membership tests are O(1).

- `SADD key member...` — add members (creates the key); duplicates are silently ignored.
- `SREM`, `SCARD` (count, O(1)), `SISMEMBER` / `SMISMEMBER` (membership, O(1)), `SMEMBERS` (all members, O(N)), `SSCAN` (iterative), `SPOP`, `SRANDMEMBER`, `SMOVE`.
- Combinations: `SINTER`, `SUNION`, `SDIFF` (and `SINTERCARD` plus the `...STORE` variants that save results to a key).

```
> SADD bikes:racing:france bike:1 bike:2 bike:3
(integer) 3
> SADD bikes:racing:usa bike:1 bike:4
(integer) 2
> SINTER bikes:racing:france bikes:racing:usa
1) "bike:1"
> SDIFF bikes:racing:france bikes:racing:usa
1) "bike:3"
2) "bike:2"
```

Max set size is 2^32 - 1 (4,294,967,295) members. `SMEMBERS` is O(n) and returns the whole set — prefer `SSCAN` for large sets. For approximate membership with low memory, consider a Bloom or Cuckoo filter (see [[concepts/probabilistic-and-geospatial]]).

## Sorted sets

A sorted set is a collection of unique strings (members) ordered by an associated floating-point score; members with equal scores are ordered lexicographically. Use cases include leaderboards and sliding-window rate limiters.

- `ZADD key score member [score member ...]` — add members or update scores (creates the key); O(log(N)) per item.
- `ZSCORE` / `ZMSCORE`, `ZINCRBY`, `ZCARD`, `ZRANK` / `ZREVRANK`, `ZCOUNT`, `ZREM`.

```
> ZADD racer_scores 10 "Norem"
(integer) 1
> ZADD racer_scores 8 "Sam-Bodden" 10 "Royce" 6 "Ford" 14 "Prickett"
(integer) 4
```

### Operating on ranges

- `ZRANGE key start stop` — members by index range (with `BYSCORE`, `BYLEX`, `REV`, `LIMIT` options); O(log(N)+M).
- `ZRANGEBYSCORE key min max` — members within a score range (`-inf`/`+inf` supported).
- `ZRANGEBYLEX` / `ZLEXCOUNT` — lexicographical range queries.
- `ZREVRANGE`, `ZRANGEBYSCORE`, `ZPOPMIN` / `ZPOPMAX` (and blocking `BZPOPMIN`/`BZPOPMAX`/`BZMPOP`), `ZREMRANGEBY*`.

```
> ZRANGEBYSCORE racer_scores -inf 10
1) "Ford"
2) "Sam-Bodden"
3) "Norem"
4) "Royce"
```

Most sorted set operations are O(log(n)); `ZRANGE` is O(log(n)+m) — use caution with large return values.

Related: [[concepts/data-types-overview]], [[concepts/probabilistic-and-geospatial]], [[concepts/json]], [[entities/redis-cli]].