Mysql 查询实现成绩排名，相同分数名次相同，类似于rank()函数
近日系统要实现总分成绩排名，而且相同分数的学生排名要一样，在网上搜了一圈，没有找到合适的方法，只能靠自己实现了，这里提供两种方法
//还有其他排名方式可以借鉴https://blog.****.net/a9925/article/details/76804951
1、sql查询实现
测试如下：
mysql> select * from score ;
+----------+--------------+---------------------+--------------+-------+
| study_no | student_name | subject_id | subject_name | score |
+----------+--------------+---------------------+--------------+-------+
| student1 | student1 | CodeCourseSubject_0 | 语文 | 120 |
| student2 | student2 | CodeCourseSubject_0 | 语文 | 110 |
| student3 | student3 | CodeCourseSubject_0 | 语文 | 110 |
| student4 | student4 | CodeCourseSubject_0 | 语文 | 80 |
| student5 | student5 | CodeCourseSubject_0 | 语文 | 81 |
| student1 | student1 | CodeCourseSubject_2 | 英语 | 150 |
| student2 | student2 | CodeCourseSubject_2 | 英语 | 130 |
| student3 | student3 | CodeCourseSubject_2 | 英语 | 130 |
| student4 | student4 | CodeCourseSubject_2 | 英语 | 44 |
| student5 | student5 | CodeCourseSubject_2 | 英语 | 45 |
+----------+--------------+---------------------+--------------+-------+
10 rows in set首先这里对科目显示进行了行列转换，并且对以学号study_no进行分组计算总分，并且按排名排序，
sql如下：
SELECT @rownum:=@rownum+1 AS rownum,
if(@total=total,@rank,@rank:=@rownum)as rank,
@total:=total,
A.*
FROM (SELECT study_no AS studyNo,
student_name AS studentName,
SUM(score) AS total,
SUM(IF(subject_id='CodeCourseSubject_0',score,0)) AS 语文,
SUM(IF(subject_id='CodeCourseSubject_2',score,0)) AS 英语
FROM score GROUP BY study_no ORDER BY total DESC
)A,(SELECT @rank:=0,@rownum:=0,@total:=null)B
结果：
+--------+------+---------------+----------+-------------+-------+-------+-------+
| rownum | rank | @total:=total | studyNo | studentName | total | 语文 | 英语 |
+--------+------+---------------+----------+-------------+-------+-------+-------+
| 1 | 1 | 270.0 | student1 | student1 | 270.0 | 120.0 | 150.0 |
| 2 | 2 | 240.0 | student2 | student2 | 240.0 | 110.0 | 130.0 |
| 3 | 2 | 240.0 | student3 | student3 | 240.0 | 110.0 | 130.0 |
| 4 | 4 | 126.0 | student5 | student5 | 126.0 | 81.0 | 45.0 |
| 5 | 5 | 124.0 | student4 | student4 | 124.0 | 80.0 | 44.0 |
+--------+------+---------------+----------+-------------+-------+-------+-------+
5 rows in set可见排名第二名有两个相同的分数，后面的排名自动往后移。
下面提供另外一种在程序中实现的方法：
2、程序实现
首先获得全班总分并且以降序排序
public List<Object[]> findAllTotalScore() {
String sql = "SELECT study_no,sum(score) AS total from score s ";
javax.persistence.Query query = em.createNativeQuery(sql);
return query.getResultList();
}
对获得的总分信息进行排序和封装成map(study_no，rank)
private Map<String, Long> rank(List<Object[]> objects) {
long previousRank = 1;
double total = 0;
//记录排名的map，map<study_no，排名>
Map<String, Long> rankMap = new HashMap<>();
for (int i = 0; i < objects.size(); i++) {
Object[] object = objects.get(i);
//计算名次，相同分数排名一样
if (total == (double) object[1]) {
rankMap.put(object[0].toString(), previousRank);
} else {
rankMap.put(object[0].toString(), i + 1L);
total = (double) object[1];
previousRank = i + 1;
}
}
return rankMap;
}
使用map直接根据学号就可以获得成绩排名。