mysql高低排名

CREATE TABLE `user_score` (
  `id` bigint(64) NOT NULL AUTO_INCREMENT,
  `userId` bigint(64) DEFAULT NULL,
  `score` double DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;
insert into `user_score` (`id`, `userId`, `score`) values('1','1','1');
insert into `user_score` (`id`, `userId`, `score`) values('2','2','20');
insert into `user_score` (`id`, `userId`, `score`) values('3','3','20');
insert into `user_score` (`id`, `userId`, `score`) values('4','4','60');
insert into `user_score` (`id`, `userId`, `score`) values('5','5','90');
insert into `user_score` (`id`, `userId`, `score`) values('6','6','100');
insert into `user_score` (`id`, `userId`, `score`) values('7','7',NULL);

SELECT 
  t1.*,
  @rank := @rank + 1 rank 
FROM
  (SELECT 
    a.`userId`,
    a.`score` 
  FROM
    `user_score` a 
  ORDER BY a.`score` DESC) t1,
  (SELECT 
    @rank := 0) t2 

SELECT 
  t1.*,
  (
    CASE
      WHEN @score  = t1.score THEN @rank 
      WHEN @score := t1.score THEN @rank := @rank + 1 
      WHEN @score  = 0 OR @score IS NULL THEN @rank := @rank + 1 
    END
  ) rank 
FROM
  (SELECT 
    userId,
    score 
  FROM
    user_score a 
  ORDER BY a.`score` DESC) t1,
  (SELECT 
    @rank := 0,
    @score := NULL) t2 ;

SELECT 
  b.userId,
  b.score,
  b.rank 
FROM
  (SELECT 
    a.*,
    @index := @index + 1,
    @rank := (
      CASE
        WHEN @temp_view_count = a.score THEN @rank 
        WHEN @temp_view_count := a.score THEN @index 
        WHEN @temp_view_count = 0  OR @temp_view_count IS NULL THEN @index 
      END
    ) rank 
  FROM
    (SELECT 
      userId,
      score 
    FROM
      user_score 
    ORDER BY score DESC) a,
    (SELECT 
      @rank := 0,
      @rowtotal := NULL,
      @index := 0) r) b