Lesson 8 / 18

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.

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.

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

Output:

1) "redis"