ZRANK命令返回成員在有序集合中的排名，基於分?jǐn)?shù)升序排列。例如，若成員“alice”得分最低，則ZRANK user_scores alice返回0；若為第三低，則返回2。當(dāng)分?jǐn)?shù)相同時，Redis按字典順序排序。若鍵或成員不存在，則返回nil。要獲取降序排名，使用ZREVRANK命令。常見註意事項包括：索引從0開始、處理分?jǐn)?shù)並列情況、確認(rèn)鍵類型為有序集合、測試是否存在用ZRANK是否返回nil。適用場景包括遊戲排行榜、用戶排名、進度條顯示等，時間複雜度為O(log N)，效率較高?？傊?，使用ZRANK時需注意其零基索引及並列排序機制，並在需要降序時使用ZREVRANK。

To get the rank of a member in a sorted set using Redis, you use the ZRANK command. It returns the zero-based index of the member based on its score in ascending order. If the key or member doesn't exist, it returns nil . That's the basic idea — now let's break down how and when to use it.

What does ZRANK actually return?

When you run ZRANK key member , Redis looks at the sorted set stored under the given key and finds where that member sits in the list ordered by score from low to high. The result is the index position — starting at 0 for the first item.

For example:

 ZRANK user_scores alice

If alice has the lowest score, this would return 0 . If she's third from the bottom, you get 2 .

• If there are ties in scores, Redis sorts members lexicographically.
• Only works with existing keys and members — otherwise, you'll get nil .

So if you're expecting a number and see nil , double-check whether the key and member both exist.

How to handle descending rank?

Redis doesn't directly support getting the rank in descending order with ZRANK . But there's a way around it: use ZREVRANK .

It works just like ZRANK , but gives you the rank as if the elements were sorted from highest to lowest.

Example:

 ZREVRANK user_scores alice

This tells you Alice's position in a leaderboard sorted from top to bottom.

So if your app shows rankings in both directions (like a game with "top players" and "bottom players"), you'll want to use both commands depending on context.

Common mistakes and things to watch out for

Here are a few gotchas people often miss:

• Index starts at 0 – Don't forget it's zero-based. So if you're displaying rankings to users, you might need to add 1 before showing the result.
• Tied scores still have order – When two members have the same score, Redis uses lexicographical ordering to determine who comes first. This can affect results unexpectedly if you don't know it.
• Check data type – Make sure the key is a sorted set. Trying to use ZRANK on a regular set or string will throw an error.
• Use ZEXISTS? No such command – To check if a member exists, just run ZRANK and see if it returns nil .

So always test with known values before relying on it in production logic.

When should you use ZRANK?

You'll find ZRANK useful whenever you need to know a member's position in a sorted collection. Common use cases include:

• Game leaderboards
• Ranking users by points, activity, or stats
• Showing progress bars or percentile ranks
• Caching and comparing relative positions without full list retrieval

Just keep in mind that ZRANK is fast — O(log N) time complexity — so even with large sets, it won't bog things down.

That's how you get a member's rank with ZRANK . Not too complicated once you understand how it indexes and handles ties. Just remember to use ZREVRANK when you need descending order and be careful with zero-based results.基本上就這些。

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