zrange

zrange is a command used with Redis sorted sets to retrieve members in a specified rank range. It returns elements ordered by their score in ascending order, optionally including their scores. zrange operates on a key that identifies a sorted set.

Syntax and parameters: ZRANGE key start stop [WITHSCORES]. key is the name of the sorted set. start and stop are integer indices, where 0 is the first element. Indices can be negative to count from the end, and the range is inclusive. When WITHSCORES is specified, the command returns a list alternating between member and score; otherwise it returns only the members.

Behavior: If the key does not exist or the set is empty, zrange returns an empty list. If the key exists but is not a sorted set, Redis returns an error. The results are always in ascending score order. Scores are stored as doubles and are returned as strings when WITHSCORES is used.

Examples: ZRANGE leaderboard 0 9 returns the first ten members by score. ZRANGE leaderboard -5 -1 WITHSCORES returns the last five members with their scores. If the sorted set contains 100 elements, ZRANGE leaderboard 0 99 returns all elements.

Performance: The operation runs in O(log(n) + m) time, where n is the number of elements in the sorted set and m is the number of elements returned. Memory usage corresponds to the number of elements retrieved.

Related commands: ZREVRANGE returns results in reverse order; ZRANGEBYSCORE and ZREVRANGEBYSCORE return elements within a score range; ZRANGEBYLEX and ZREVRANGEBYLEX operate on lexicographic order of members.