What are ZADD and ZRANGE in Redis?

ZADD key score member adds a member with a numeric score to a Redis Sorted Set. Members are unique but scores can repeat; members are always stored in ascending score order. ZRANGE key start stop retrieves members by index range in ascending score order; add REV for descending. For leaderboards, ZREVRANGE key 0 9 returns the top 10 highest-scoring members. ZRANK key member returns a member's rank (0-based). ZSCORE key member gets a member's score. ZINCRBY key amount member atomically updates a score, making it perfect for live leaderboards where game scores update frequently. Sorted Sets are the go-to data structure for any ranking, scoring, or priority queue use case in Redis.