心得

題目要求找出成績排名，如果分數相同的話則相同名次，MySQL不像MSSQL有ROW_NUMBER()可以用，只好用個變數來存了。

問題

Write a SQL query to rank scores. If there is a tie between two scores, both should have the same ranking. Note that after a tie, the next ranking number should be the next consecutive integer value. In other words, there should be no “holes” between ranks.

+----+-------+
| Id | Score |
+----+-------+
| 1  | 3.50  |
| 2  | 3.65  |
| 3  | 4.00  |
| 4  | 3.85  |
| 5  | 4.00  |
| 6  | 3.65  |
+----+-------+

For example, given the above Scores table, your query should generate the following report (order by highest score):

+-------+------+
| Score | Rank |
+-------+------+
| 4.00  | 1    |
| 4.00  | 1    |
| 3.85  | 2    |
| 3.65  | 3    |
| 3.65  | 3    |
| 3.50  | 4    |
+-------+------+

答案

# Write your MySQL query statement below
SELECT a.Score, b.Rank
FROM Scores AS a
JOIN (SELECT (@row_number:=@row_number + 1) AS Rank, z.Score
      FROM (SELECT x.* 
            FROM Scores AS x 
            GROUP BY x.Score
            ORDER BY x.Score DESC) AS z
      JOIN (SELECT @row_number := 0) AS y) AS b
ON a.Score = b.Score  
ORDER BY `b`.`Score` DESC