Top-N queries in Redis

Introduction

Top-N queries help you find the highest or lowest N items from a list, like the top 5 scores or best-selling products.

Showing the top 3 players with the highest scores in a game.

Finding the 10 most popular products in an online store.

Listing the 5 most recent posts with the most likes.

Getting the top 7 cities with the highest temperatures today.

Syntax

Redis

ZRANGE key start stop [WITHSCORES]
ZREVRANGE key start stop [WITHSCORES]

ZRANGE returns items in ascending order (lowest to highest score).

ZREVRANGE returns items in descending order (highest to lowest score).

Examples

Get the bottom 5 items with their scores from the sorted set 'leaderboard'.

Redis

ZRANGE leaderboard 0 4 WITHSCORES

Get the top 3 items with their scores from the sorted set 'leaderboard'.

Redis

ZREVRANGE leaderboard 0 2 WITHSCORES

Sample Program

Add 5 players with scores to 'leaderboard'. Then get the top 3 players with highest scores.

Redis

ZADD leaderboard 100 Alice 200 Bob 150 Carol 180 Dave 120 Eve
ZREVRANGE leaderboard 0 2 WITHSCORES

Important Notes

Sorted sets in Redis store members with scores, allowing easy Top-N queries.

Indexes start at 0, so 0 2 means first 3 items.

WITHSCORES option returns both member and its score.

Summary

Top-N queries find the highest or lowest N items in a sorted set.

Use ZREVRANGE for top scores (descending order).

Use ZRANGE for lowest scores (ascending order).