Master Redis: Explore All 8 Data Types and Essential Commands

NoSQL development often involves Redis, a key‑value store that appears frequently in interview questions.

Recent interviews have highlighted the need to master its data structures; this article consolidates essential Redis knowledge.

Redis’s Eight Data Types

String (字符串)

Basic key‑value type. Supports set, get, append, incr/decr, range, setrange, setex, setnx, mset/mget, getset, etc.

127.0.0.1:6379> keys *
(empty list or set)
127.0.0.1:6379> set name xxx
OK
127.0.0.1:6379> keys *
1) "name"
127.0.0.1:6379> set age 1
OK
127.0.0.1:6379> keys *
1) "age"
2) "name"
127.0.0.1:6379> exists name   # 判断key是否存在 (integer) 1
127.0.0.1:6379> move name 1   # 将key移动到指定db (integer) 1
127.0.0.1:6379> expire name 10   # 设置key的过期时间，单位秒 (integer) 1
127.0.0.1:6379> ttl name   # 查看剩余过期时间 (integer) 7
127.0.0.1:6379> type age   # 查看key类型，返回string

Typical scenarios: counters, statistics, fan counts, object caching.

List (列表)

Ordered collection, usable as stack, queue, or blocking queue. Most commands start with l.

127.0.0.1:6379> lpush list one   # left push
127.0.0.1:6379> lpush list two
127.0.0.1:6379> lpush list three
127.0.0.1:6379> lrange list 0 -1   # view all elements
1) "three"
2) "two"
3) "one"
127.0.0.1:6379> rpush list right   # right push
127.0.0.1:6379> lrange list 0 -1
1) "three"
2) "two"
3) "one"
4) "right"
127.0.0.1:6379> lpop list   # pop from left
"three"
127.0.0.1:6379> rpop list   # pop from right
"right"
127.0.0.1:6379> lindex list 1   # get element by index
"two"
127.0.0.1:6379> llen list   # length
(integer) 2
127.0.0.1:6379> lrem list 1 world   # remove specific value
(integer) 1
127.0.0.1:6379> ltrim mylist 1 2   # keep elements 1~2

Key points: list is a linked list; insertion at both ends is O(1); empty list is considered non‑existent.

Set (集合)

Unordered collection of unique strings.

127.0.0.1:6379> sadd myset "hello"
(integer) 1
127.0.0.1:6379> sadd myset "world"
(integer) 1
127.0.0.1:6379> smembers myset
1) "world"
2) "hello"
127.0.0.1:6379> sismember myset hello
(integer) 1
127.0.0.1:6379> scard myset   # cardinality
(integer) 2
127.0.0.1:6379> srem myset hello   # remove element
(integer) 1

Set operations: union, intersection, difference, random member, move between sets.

Hash (哈希)

Map of field‑value pairs stored under a single key.

127.0.0.1:6379> hset myhash field xxx
(integer) 1
127.0.0.1:6379> hget myhash field
"xxx"
127.0.0.1:6379> hmset myhash field1 hello field2 world
OK
127.0.0.1:6379> hgetall myhash
1) "field"
2) "xxx"
3) "field1"
4) "hello"
5) "field2"
6) "world"
127.0.0.1:6379> hdel myhash field1
(integer) 1
127.0.0.1:6379> hincrby myhash field3 1   # increment numeric field
(integer) 6

Ideal for storing mutable objects; strings are better for plain text.

Sorted Set (zset, 有序集合)

Set of unique members with a floating‑point score, enabling range queries by score.

127.0.0.1:6379> zadd myset 1 one
(integer) 1
127.0.0.1:6379> zadd myset 2 two 3 three
(integer) 2
127.0.0.1:6379> zrange myset 0 -1
1) "one"
2) "two"
3) "three"
127.0.0.1:6379> zadd salary 2500 xiaohong
(integer) 1
127.0.0.1:6379> zadd salary 5000 xiaoming
(integer) 1
127.0.0.1:6379> zrangebyscore salary -inf +inf withscores
1) "xaiozhang"
2) "500"
3) "xiaohong"
4) "2500"
5) "xiaoming"
6) "5000"
127.0.0.1:6379> zrem salary xiaohong   # remove member
(integer) 1
127.0.0.1:6379> zcard salary   # cardinality
(integer) 2

Geospatial

Introduced in Redis 3.2, stores longitude/latitude as a sorted set.

127.0.0.1:6379> geoadd china:city 116.40 39.90 beijing
(integer) 1
127.0.0.1:6379> geopos china:city beijing
1) 1) "116.39999896287918091"
   2) "39.90000009167092543"
127.0.0.1:6379> geodist china:city beijing shanghai km
"1067.3788"
127.0.0.1:6379> georadius china:city 110 30 1000 km
1) "chongqing"
2) "xian"

Underlying implementation uses a sorted set, so all ZSET commands apply.

HyperLogLog

Probabilistic data structure for cardinality estimation with fixed 12 KB memory.

127.0.0.1:6379> pfadd mykey a b c d e f g h i j
(integer) 1
127.0.0.1:6379> pfcount mykey
(integer) 10
127.0.0.1:6379> pfadd mykey2 i j z x c v b n m
(integer) 1
127.0.0.1:6379> pfcount mykey2
(integer) 9
127.0.0.1:6379> pfmerge mykey3 mykey mykey2
OK
127.0.0.1:6379> pfcount mykey3
(integer) 15

Bitmap

Bit‑level representation for boolean flags, useful for daily sign‑in, UV counting, etc.

127.0.0.1:6379> setbit sign 0 1   # Monday signed
(integer) 0
127.0.0.1:6379> setbit sign 3 1   # Thursday signed
(integer) 0
127.0.0.1:6379> getbit sign 3
(integer) 1
127.0.0.1:6379> bitcount sign
(integer) 4   # total signed days