How to reverse lookup in redis?

@addison 

In Redis, there is no built-in command to perform a reverse lookup directly. However, you can achieve reverse lookup by using secondary indexes or maintaining a reverse index yourself.

Here are a few ways to perform a reverse lookup in Redis:

1. Using secondary indexes: You can maintain secondary indexes for the values you want to lookup by creating separate keys that map values to keys in a reverse index. For example, if you have a key-value pair in Redis like "user:1234" => "alice", you can create a secondary index key "username:alice" => "1234" to perform reverse lookup by username.
2. Using sets: You can use sets in Redis to maintain reverse indexes. For example, you can create a set "usernames:alice" and store the keys of users with the username "alice" in the set. You can then use the SMEMBERS command to get all the keys in the set.
3. Using sorted sets: You can also use sorted sets in Redis to maintain reverse indexes with scores. For example, you can create a sorted set "usernames" and add the username as the member and the key as the score. You can then use ZRANGE or ZREVRANGE command to perform reverse lookup.

Overall, reverse lookup in Redis requires some additional data structure and maintenance to achieve efficiently. Choose the method that fits your use case best based on your requirements for performance, memory usage, and ease of maintenance.