create table scores_tb (
 id int auto_increment primary key,
 xuehao int not null, 
 score int not null
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
insert into scores_tb (xuehao,score) values (1001,89),(1002,99),(1003,96),(1004,96),(1005,92),(1006,90),(1007,90),(1008,94);

# 查看下插入的数据
mysql> select * from scores_tb;
+----+--------+-------+
| id | xuehao | score |
+----+--------+-------+
| 1 | 1001 | 89 |
| 2 | 1002 | 99 |
| 3 | 1003 | 96 |
| 4 | 1004 | 96 |
| 5 | 1005 | 92 |
| 6 | 1006 | 90 |
| 7 | 1007 | 90 |
| 8 | 1008 | 94 |
+----+--------+-------+

# 查询语句
SELECT xuehao, score, @curRank := @curRank + 1 AS rank
FROM scores_tb, (
SELECT @curRank := 0
) r
ORDER BY score desc;

# 排序结果
+--------+-------+------+
| xuehao | score | rank |
+--------+-------+------+
| 1002 | 99 | 1 |
| 1003 | 96 | 2 |
| 1004 | 96 | 3 |
| 1008 | 94 | 4 |
| 1005 | 92 | 5 |
| 1006 | 90 | 6 |
| 1007 | 90 | 7 |
| 1001 | 89 | 8 |
+--------+-------+------+

# 查询语句
SELECT xuehao, score, 
CASE
WHEN @prevRank = score THEN @curRank
WHEN @prevRank := score THEN @curRank := @curRank + 1
END AS rank
FROM scores_tb, 
(SELECT @curRank :=0, @prevRank := NULL) r
ORDER BY score desc;

# 排名结果
+--------+-------+------+
| xuehao | score | rank |
+--------+-------+------+
| 1002 | 99 | 1 |
| 1003 | 96 | 2 |
| 1004 | 96 | 2 |
| 1008 | 94 | 3 |
| 1005 | 92 | 4 |
| 1006 | 90 | 5 |
| 1007 | 90 | 5 |
| 1001 | 89 | 6 |
+--------+-------+------+

# 查询语句
SELECT xuehao, score, rank FROM
(SELECT xuehao, score,
@curRank := IF(@prevRank = score, @curRank, @incRank) AS rank, 
@incRank := @incRank + 1, 
@prevRank := score
FROM scores_tb, (
SELECT @curRank :=0, @prevRank := NULL, @incRank := 1
) r
ORDER BY score desc) s;
# 排名结果
+--------+-------+------+
| xuehao | score | rank |
+--------+-------+------+
| 1002 | 99 | 1 |
| 1003 | 96 | 2 |
| 1004 | 96 | 2 |
| 1008 | 94 | 4 |
| 1005 | 92 | 5 |
| 1006 | 90 | 6 |
| 1007 | 90 | 6 |
| 1001 | 89 | 8 |
+--------+-------+------+

# 三条语句对于上面三种排名
select xuehao,score, ROW_NUMBER() OVER(order by score desc) as row_r from scores_tb;
select xuehao,score, DENSE_RANK() OVER(order by score desc) as dense_r from scores_tb;
select xuehao,score, RANK() over(order by score desc) as r from scores_tb;

# 一条语句也可以查询出不同排名
SELECT xuehao,score,
 ROW_NUMBER() OVER w AS 'row_r',
 DENSE_RANK() OVER w AS 'dense_r',
 RANK()  OVER w AS 'r'
FROM `scores_tb`
WINDOW w AS (ORDER BY `score` desc);

# 排名结果
+--------+-------+-------+---------+---+
| xuehao | score | row_r | dense_r | r |
+--------+-------+-------+---------+---+
| 1002 | 99 |  1 |  1 | 1 |
| 1003 | 96 |  2 |  2 | 2 |
| 1004 | 96 |  3 |  2 | 2 |
| 1008 | 94 |  4 |  3 | 4 |
| 1005 | 92 |  5 |  4 | 5 |
| 1006 | 90 |  6 |  5 | 6 |
| 1007 | 90 |  7 |  5 | 6 |
| 1001 | 89 |  8 |  6 | 8 |
+--------+-------+-------+---------+---+