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ZRANGEBYSCORE

Introduction​

In Dragonfly, as well as in Redis and Valkey, the ZRANGEBYSCORE command is used to return all members in a sorted set with scores within the given range. This command is particularly useful when working with time-series data, leaderboards, or prioritization algorithms.

Syntax​

ZRANGEBYSCORE key min max [WITHSCORES] [LIMIT offset count]
  • Time complexity: O(log(N)+M) with N being the number of elements in the sorted set and M the number of elements being returned. If M is constant (e.g. always asking for the first 10 elements with LIMIT), you can consider it O(log(N)).
  • ACL categories: @read, @sortedset, @slow

Parameter Explanations​

  • key: The name of the sorted set from which members will be retrieved.
  • min: The minimum score for the range query.
  • max: The maximum score for the range query.
  • WITHSCORES (optional): If present, the command returns both members and their scores.
  • LIMIT offset count (optional): Limits the number of results to count starting from the offset. Used for pagination.

Return Values​

The command returns an array of the members in the specified score range. If WITHSCORES is provided, members and their scores are returned as alternating values in the array.

Code Examples​

Basic Example​

Return members with scores between 10 and 30 from a sorted set:

dragonfly> ZADD myzset 10 "a" 20 "b" 30 "c" 40 "d"
(integer) 4
dragonfly> ZRANGEBYSCORE myzset 10 30
1) "a"
2) "b"
3) "c"

Using WITHSCORES​

Retrieve members with scores between 10 and 30, including the scores:

dragonfly> ZRANGEBYSCORE myzset 10 30 WITHSCORES
1) "a"
2) "10"
3) "b"
4) "20"
5) "c"
6) "30"

Using LIMIT​

Limit the result to 2 members, starting from the second one (offset = 1):

dragonfly> ZRANGEBYSCORE myzset 10 40 LIMIT 1 2
1) "b"
2) "c"

Exclusive Ranges​

You can use ( to denote an open (exclusive) bound for the score range. For example, only return members with scores greater than 10 but less than or equal to 30:

dragonfly> ZRANGEBYSCORE myzset (10 30
1) "b"
2) "c"

Best Practices​

  • Use LIMIT for pagination when dealing with large sets to reduce memory usage and improve performance.
  • Combine ZRANGEBYSCORE with WITHSCORES to retrieve both the values and their scores in one command, providing better efficiency.

Common Mistakes​

  • Misunderstanding that the LIMIT clause is applied after the score filtering, meaning it limits how many results are returned but does not affect the score range.
  • Confusing min and max values: min must always be less than or equal to max.

FAQs​

Can ZRANGEBYSCORE return members with equal scores?​

Yes, if multiple members have the same score, all of them within the given score range will be returned.

What happens if no members match the score range?​

If no members fall within the specified score range, an empty array is returned.

Can I specify negative infinity as a min or max?​

Yes, -inf and +inf can be used as min and max respectively, allowing you to retrieve all members below or above certain score thresholds. For example:

dragonfly> ZRANGEBYSCORE myzset -inf 20
1) "a"
2) "b"