redis笔记（String）

猫子哥

Feb 16·7 min read

由于memcache的局限性，诞生了redis，相比较memcache中的value，redis中的value有了数据类型的区分，redis对每种类型都有响应的操作方法，使用起来更加灵活。目前redis是最流行的内存nosql数据库。

数据类型

String

Redis中支持的String包含字符，数值，bitmaps。可以通过OBJECT命令查看encoding。

127.0.0.1:6379> OBJECT help
1) OBJECT <subcommand> arg arg ... arg. Subcommands are:
2) ENCODING <key> -- Return the kind of internal representation used in order to store the value associated with a key.
3) FREQ <key> -- Return the access frequency index of the key. The returned integer is proportional to the logarithm of the recent access frequency of the key.
4) IDLETIME <key> -- Return the idle time of the key, that is the approximated number of seconds elapsed since the last access to the key.
5) REFCOUNT <key> -- Return the number of references of the value associated with the specified key.

例如：

127.0.0.1:6379> set key1 1
OK
127.0.0.1:6379> object encoding key1
"int"

最基本的命令GET和SET，用来设置和获取一个key的value。

GET key
  summary: Get the value of a key
  since: 1.0.0

  SET key value [EX seconds|PX milliseconds|KEEPTTL] [NX|XX]
  summary: Set the string value of a key
  since: 1.0.0

举个🌰：

127.0.0.1:6379> set rediskey 'hello world'
OK
127.0.0.1:6379> get rediskey
"hello world"

APPEND命令，用来给一个key附加value

APPEND key value
  summary: Append a value to a key
  since: 2.0.0

再举个🌰：

127.0.0.1:6379> append rediskey 'heihei'
(integer) 17
127.0.0.1:6379> get rediskey
"hello worldheihei"

INCR命令，给一个key的int值加1

INCR key
  summary: Increment the integer value of a key by one
  since: 1.0.0

依旧举个🌰：

127.0.0.1:6379> set intvalue 1
OK
127.0.0.1:6379> incr intvalue
(integer) 2
127.0.0.1:6379> get intvalue
"2"

DECR命令，给一个key的int值减1

DECR key
  summary: Decrement the integer value of a key by one
  since: 1.0.0

还得要举个🌰：

127.0.0.1:6379> get intvalue
"2"
127.0.0.1:6379> decr intvalue
(integer) 1

INCRBY命令，给一个key的int值加上给定的数值

INCRBY key increment
  summary: Increment the integer value of a key by the given amount
  since: 1.0.0

这里举个🌰：

127.0.0.1:6379> get intvalue
"1"
127.0.0.1:6379> incrby intvalue 2
(integer) 3
127.0.0.1:6379> get intvalue
"3"

DECRBY命令，给一个key的int值减去给定的数值

DECRBY key decrement
  summary: Decrement the integer value of a key by the given number
  since: 1.0.0

这儿有个🌰：

127.0.0.1:6379> get intvalue
"3"
127.0.0.1:6379> decrby intvalue 2
(integer) 1
127.0.0.1:6379> get intvalue
"1"

GETSET命令，给一个key设置一个value，并返回旧值

GETSET key value
  summary: Set the string value of a key and return its old value
  since: 1.0.0

依旧要举个🌰：

127.0.0.1:6379> get rediskey
"hello worldheihei"
127.0.0.1:6379> getset rediskey 'hello redis'
"hello worldheihei"
127.0.0.1:6379> get rediskey
"hello redis"

MGET MSET命令，批量get和set value

MGET key [key ...]
  summary: Get the values of all the given keys
  since: 1.0.0

  MSET key value [key value ...]
  summary: Set multiple keys to multiple values
  since: 1.0.1

让我举个🌰：

127.0.0.1:6379> MSET key1 'key1' key2 'key2' key3 'key3'
OK
127.0.0.1:6379> MGET key1 key2 key3
1) "key1"
2) "key2"
3) "key3"

位图bitmap

设置一个位图使用SETBIT命令，参数为key,offset(二进制位的偏移量),value

一个字节有8个二进制位，offset对于多个字节是连续的

比如设置k1偏移量为1的位置为1，获取到ascii码中对应的01000000的值@

BITPOS命令，查找一个bit值在一个String中第一个偏移量，比如上面的k1，0到1这两个字节之间第一个1的位置为1

BITCOUNT命令，返回字节区间内，bit的count数，比如上面的k1，有1个1

BITOP命令，两个位图进行逻辑与或的操作