hexists(hash exists) 判断指定key中的字段是否存在

127.0.0.1:6379> hgetall user:1
1) "name"
2) "youyi"
3) "age"
4) "20"
127.0.0.1:6379> hexists user:1 name
(integer) 1
127.0.0.1:6379> hexists user:1 na
(integer) 0