doc: 阅读redis sets文档

中间件/redis/redis.md

@@ -56,6 +56,15 @@
       - [Blocking operations on lists](#blocking-operations-on-lists)
         - [BRPOP](#brpop)
       - [Automatic Creation and removal of keys](#automatic-creation-and-removal-of-keys)
+    - [redis sets](#redis-sets)
+      - [basic commands](#basic-commands)
+      - [SADD](#sadd)
+      - [SMEMBERS](#smembers)
+      - [SDIFF](#sdiff)
+      - [SINTER](#sinter)
+      - [SREM](#srem)
+      - [SPOP](#spop)
+      - [SRANDMEMBER](#srandmember)
 
 
 # redis
@@ -851,3 +860,93 @@ client 2> rpush event-queue:2 baka
 > LPOP bikes:repairs
 (nil)
 ```
+
+### redis sets
+redis set是一个unordered collection of unique strings，通过redis sets可以高效进行如下操作：
+- track unique items
+- represent relations
+- perform common set operations such as intersection, unions, and differences
+
+#### basic commands
+- `SADD`: 向set中添加new member
+- `SREM`: 从set中移除指定member
+- `SISMEMBER`: 检查给定的string是否位于set中
+- `SINTER`: 返回两个或更多set的交集
+- `SCARD`: 返回set的大小（cardinality）
+
+#### SADD
+`SADD`命令会向set中添加新的元素，示例如下：
+```redis-cli
+> SADD bikes:racing:france bike:1 bike:2 bike:3
+(integer) 3
+> SMEMBERS bikes:racing:france
+1) bike:3
+2) bike:1
+3) bike:2
+```
+#### SMEMBERS
+在上述示例中，`SMEMBERS`命令会返回set中所有的元素。`redis`并不保证元素的返回顺序，每次调用`SMEMBERS`命令都可能以任何顺序返回set中的元素。
+
+#### SDIFF
+可以通过SDIFF来返回两个sets的差异（差集）。例如，可以通过`SDIFF`命令查看有哪些元素位于`set1`中但是不位于`set2`中，示例如下：
+```redis-cli
+> SADD bikes:racing:usa bike:1 bike:4
+(integer) 2
+> SDIFF bikes:racing:france bikes:racing:usa
+1) "bike:3"
+2) "bike:2"
+```
+上述示例中，则通过`SDIFF`命令展示了`bikes:racing:france`和`bikes:racing:usa`两个set的差集。
+
+SDIFF命令在`difference between all sets is empty`时，会返回一个empty array。
+
+#### SINTER
+可以通过SINTER命令来取多个sets的交集。
+
+```redis-cli
+> SADD bikes:racing:france bike:1 bike:2 bike:3
+(integer) 3
+> SADD bikes:racing:usa bike:1 bike:4
+(integer) 2
+> SADD bikes:racing:italy bike:1 bike:2 bike:3 bike:4
+(integer) 4
+> SINTER bikes:racing:france bikes:racing:usa bikes:racing:italy
+1) "bike:1"
+> SUNION bikes:racing:france bikes:racing:usa bikes:racing:italy
+1) "bike:2"
+2) "bike:1"
+3) "bike:4"
+4) "bike:3"
+> SDIFF bikes:racing:france bikes:racing:usa bikes:racing:italy
+(empty array)
+> SDIFF bikes:racing:france bikes:racing:usa
+1) "bike:3"
+2) "bike:2"
+> SDIFF bikes:racing:usa bikes:racing:france
+1) "bike:4"
+```
+#### SREM
+可以通过`SREM`命令来移除set中的元素，可以一次性移除一个或多个。
+
+#### SPOP
+`SPOP`命令支持随机移除一个element。
+
+#### SRANDMEMBER
+`SRANDMEMBER`命令支持随机返回一个set中的元素，但是不对其实际移除
+
+上述命令的使用示例如下所示：
+```redis-cli
+> SADD bikes:racing:france bike:1 bike:2 bike:3 bike:4 bike:5
+(integer) 5
+> SREM bikes:racing:france bike:1
+(integer) 1
+> SPOP bikes:racing:france
+"bike:3"
+> SMEMBERS bikes:racing:france
+1) "bike:2"
+2) "bike:4"
+3) "bike:5"
+> SRANDMEMBER bikes:racing:france
+"bike:2"
+```
+