leetcode Database3
一、Rank Scores
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 |
+-------+------+
分析:题意为 编写SQL对分数进行排序。如果两个分数相等,其排名应相同。注意在排名相等的分数之后,下一个排名的数值应该连续。换言之,排名之间不应该有“洞”(跳跃)。
思路:使用mysql的自定义变量。
# Write your MySQL query statement below
select Score,Rank from
(
SELECT Score,
CASE
WHEN @dummy <=> Score THEN @Rank := @Rank
ELSE @Rank := @Rank +1
END AS Rank,@dummy := Score as dummy
FROM
(SELECT @Rank := 0,@dummy := NULL) r,
Scores
ORDER BY Score DESC
) AS C
或者:
# Write your MySQL query statement below
SELECT Scores.Score, COUNT(Ranking.Score) AS RANK
FROM Scores
, (
SELECT DISTINCT Score
FROM Scores
) Ranking
WHERE Scores.Score <= Ranking.Score
GROUP BY Scores.Id, Scores.Score
ORDER BY Scores.Score DESC;
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