ZRANK
Syntax
        ZRANK key member
- Available since:
- 2.0.0
- Time complexity:
- O(log(N))
- ACL categories:
- 
              
                @read,@sortedset,@fast,
Returns the rank of member in the sorted set stored at key, with the scores
ordered from low to high.
The rank (or index) is 0-based, which means that the member with the lowest
score has rank 0.
Use ZREVRANK to get the rank of an element with the scores ordered from high
to low.
Return
- If memberexists in the sorted set, Integer reply: the rank ofmember.
- If memberdoes not exist in the sorted set orkeydoes not exist, Bulk string reply:nil.