Introduction to Redis data structures: strings, hashes, lists, sets, ordered sets

Redis is an efficient open source in-memory data storage system that supports rich data structures. This article will introduce the five basic data structures supported by Redis: string, hash, list, set, and ordered set.

1. String (string)
   String is the most basic data structure of Redis and the simplest. Redis strings can store any type of data, such as numbers, binary data, even pictures, videos, etc. Normally, strings in Redis store key-value pair data in text form.

The operations supported by the string type include Set, Get, Incrby, etc. Among them, Set supports storing a new string in Redis, Get supports obtaining a stored string from Redis, and Incrby supports incrementing a numeric string stored in Redis. At the same time, the string type also supports some special operations, such as Append, Getrange, etc.

2. Hash(hash)
   Hash table is a common storage structure in data structures that allows you to obtain values ​​by key. In Redis, a hash table is a mapping relationship between string keys and string values. Each hash table can store up to 430 million key-value pairs.

The operations supported by the hash type include Hset, Hget, Hincrby, etc. Among them, Hset supports storing a new hash item in Redis, Hget supports obtaining the value of a stored hash item from Redis, and Hincrby supports incrementing the value of an integer hash item stored in Redis. In addition, the hash type also supports some other operations, such as Hmset, Hgetall, etc.

3. List(list)
   A list is an ordered data structure. A list in Redis refers to an ordered collection of string type elements, which can support operations such as insertion, deletion and query. .

The operations supported by the list type include Lpush, Rpush, Lpop, Rpop, etc. Among them, Lpush and Rpush support inserting an element at the head or tail of the list, and Lpop and Rpop support deleting an element from the head or tail of the list. In addition, the list type also supports some other operations, such as Lrange, Ltrim, etc.

4. Set (set)
   A set is different from a list in that it is unordered. In Redis, a set is also an unordered collection of string type elements. The operations supported by the collection type include Sadd, Srem, Sismember, Smembers, etc. Among them, Sadd and Srem support adding or deleting an element to the collection, Sismember supports querying whether the collection contains an element, and Smembers supports obtaining all elements in the collection. In addition, the collection type also supports some other operations, such as Scard, Sinter, etc.
5. Ordered set (sorted set)
   Ordered set is different from the previously introduced set in that each element has an associated score and is sorted according to the score. In Redis, an ordered set is also an ordered collection of string type elements.

The operations supported by the ordered set type include Zadd, Zrem, Zscore, Zrange, etc. Among them, Zadd and Zrem support adding or deleting an element to an ordered set, Zscore supports querying the score of an element in an ordered set, and Zrange supports querying elements within a certain range in an ordered set. In addition, the ordered set type also supports some other operations, such as Zrank, Zcount, etc.

Summary
The above five basic data structures are commonly used in Redis, and their usage scenarios are different. By rationally selecting and using these data structures flexibly, Redis can play a greater role in practical applications.

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