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ZREVRANK

Introduction and Use Case(s)​

The ZREVRANK command in Redis returns the rank of a member in a sorted set, with the scores ordered from high to low. It is particularly useful for reverse ranking scenarios, such as leaderboard systems where you want to know the position of a participant based on their score.

Syntax​

ZREVRANK key member

Parameter Explanations​

  • key: The name of the sorted set.
  • member: The member whose rank you wish to retrieve.

These parameters are essential for identifying which sorted set and member you are querying.

Return Values​

  • Integer: The rank of the member (0-based index).
  • nil: If the member does not exist within the sorted set.

Example Outputs:​

  • (integer) 0 when the member is the highest-scoring member.
  • (nil) when the member is not found in the sorted set.

Code Examples​

dragonfly> ZADD myzset 1 "one"
(integer) 1
dragonfly> ZADD myzset 2 "two"
(integer) 1
dragonfly> ZADD myzset 3 "three"
(integer) 1
dragonfly> ZREVRANK myzset "one"
(integer) 2
dragonfly> ZREVRANK myzset "three"
(integer) 0
dragonfly> ZREVRANK myzset "four"
(nil)

Best Practices​

  • Ensure that the sorted set (key) exists before calling ZREVRANK to avoid unnecessary nil results.
  • Use this command in operations where reverse ranking based on scores is critical, like high-score tables in gaming applications.

Common Mistakes​

  • Misinterpreting the 0-based index: A rank of (integer) 0 means the member has the highest score.
  • Forgetting that ZREVRANK returns nil if the member does not exist, which can lead to unhandled exceptions in some applications.

FAQs​

Q: What happens if the sorted set does not exist?

A: The command will simply return nil, indicating that the member was not found.

Q: Can ZREVRANK handle negative scores?

A: Yes, ZREVRANK ranks members based on their scores regardless of whether the scores are positive or negative.