Sets
Unique members
Sets ignore duplicates—ideal for tags, unique visitors, or ID collections.
SADD post:1:tags redis cache
SADD post:1:tags redis
SMEMBERS post:1:tags
SISMEMBER post:1:tags cacheCombine sets
Union, intersection, and difference answer set questions quickly.
SADD a 1 2 3
SADD b 3 4
SINTER a b
SUNION a b
SDIFF a bPop and size
SCARD counts members; SPOP removes a random member.
SCARD post:1:tags
SPOP post:1:tagsSorted sets next
When you need uniqueness plus a score (leaderboards), use sorted sets (ZADD).
ZADD scores 100 alice 95 bob
ZREVRANGE scores 0 2 WITHSCORES
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