# Sets — Redis

Source: https://www.geekswithgeeks.com/en/redis/redis-sets

> Unordered, unique members — built for membership checks and set math.

## SADD & SMEMBERS

A **set** stores each value once. `SISMEMBER` checks membership in constant time — no scanning needed.

```bash
SADD tags:post:9 "redis" "cache" "redis"
SMEMBERS tags:post:9
SISMEMBER tags:post:9 "cache"
```

Output:

```
(integer) 2
1) "redis"
2) "cache"
(integer) 1
```

## Set operations

Redis computes intersections and unions server-side — useful for "mutual friends" or "common tags" style features.

```bash
SADD tags:post:9 "redis" "cache"
SADD tags:post:12 "redis" "db"
SINTER tags:post:9 tags:post:12
```

Output:

```
1) "redis"
```