Top-N queries in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Top-N query in Redis?

A Top-N query in Redis retrieves the top N elements from a sorted set based on their scores, usually to find the highest or lowest ranked items.

beginner

Which Redis data structure is commonly used for Top-N queries?

Sorted Sets (ZSET) are used because they store elements with scores, allowing efficient retrieval of top N elements by score order.

beginner

How do you get the top 5 highest scored elements from a sorted set named 'leaderboard' in Redis?

Use the command: ZREVRANGE leaderboard 0 4 WITHSCORES. This gets elements with highest scores first, from rank 0 to 4.

beginner

What does the Redis command ZREVRANGE do?

ZREVRANGE returns elements in a sorted set ordered from highest to lowest score, useful for Top-N queries to get top scoring items.

intermediate

Why is using sorted sets efficient for Top-N queries in Redis?

Because sorted sets keep elements ordered by score, Redis can quickly return the top N elements without scanning the entire set.

Which Redis command retrieves the top N elements with the highest scores from a sorted set?

A ZREVRANGE

B ZRANGE

C ZADD

D ZREM

ZREVRANGE returns elements ordered from highest to lowest score, perfect for Top-N queries.

What data structure should you use in Redis to perform Top-N queries?

A List

B Hash

C String

D Sorted Set

Sorted Sets store elements with scores and keep them ordered, ideal for Top-N queries.

If you want the top 3 lowest scored elements in Redis, which command would you use?

A ZREVRANGE key 0 2

B ZADD key 0 2

C ZRANGE key 0 2

D ZREM key 0 2

ZRANGE returns elements ordered from lowest to highest score, so it gets the lowest scored elements.

What does the WITHSCORES option do in ZREVRANGE or ZRANGE commands?

A Deletes the scores

B Returns elements with their scores

C Returns elements only

D Adds new elements

WITHSCORES makes Redis return each element along with its score.

Why are Top-N queries fast in Redis sorted sets?

A Because sorted sets keep elements ordered by score

B Because Redis scans all elements

C Because Redis uses hash tables

D Because Redis stores data on disk

Sorted sets maintain order by score, so Redis can quickly access top elements without scanning all data.

Explain how you would retrieve the top 10 highest scoring players from a Redis leaderboard using sorted sets.

Think about commands that return elements ordered by score descending.

Describe why sorted sets are suitable for Top-N queries in Redis compared to other data structures.

Consider how ordering and score storage help performance.