Leetcode Day1 score ranking

Mysql

178. Score ranking

Medium difficulty

SQL framework

Write a SQL Query to achieve score ranking .

If two scores are the same , Then two scores rank （Rank） identical . Please note that , The next rank after bisection should be the next consecutive integer value . let me put it another way , There should not be between ranks “ interval ”.

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

for example , According to the... Given above Scores surface , Your query should return （ Rank by score from high to low ）：

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

** Important note ：** about MySQL Solution , If you want to escape a reserved word used as a column name , You can use apostrophes before and after keywords . for example Rank

Answer key 1： Special window functions dense_rank

select `Score`,
dense_rank() over (Order by Score desc) as `Rank` 
from Scores;

Running results ：

dense_rank Lines with parallel ranks in functions will not occupy the position of the next name , That is to say 1、1、2、3、3、4. Rank like this .

Expand ：

mysql Four sorting functions ：

Example ：

select `Score`,
dense_rank() over (Order by Score desc) as `Rank` ,
rank() over (Order by Score desc) as `Rank1`,
row_number() over (Order by Score desc) as `Rank2`
from Scores;

Running results ：

According to the running results :

1、rank function ： result 1、1、3、4、4、6 That is, if there is a row with parallel ranking , Will occupy the next place .

2、dense_rank function ： result ：1、1、2、3、3、4, That is, if there is a row with parallel ranking , Don't occupy the next place .

3、row_number function ： result 1、2、3、4、5、6, That is, regardless of the parallel ranking .

The fourth sorting function is :

Example ：

select `Score`,
ntile(1) over (Order by Score desc) as `Rank1`,
ntile(2) over (Order by Score desc) as `Rank2`,
ntile(3) over (Order by Score desc) as `Rank3`,
ntile(4) over (Order by Score desc) as `Rank4`,
ntile(5) over (Order by Score desc) as `Rank5`,
ntile(6) over (Order by Score desc) as `Rank6`,
ntile(7) over (Order by Score desc) as `Rank7`
from Scores;

result ：

ntile(1) : result 1、1、1、1、1、1

ntile(2) : result 1、1、1、2、2、2

ntile(3) : result 1、1、2、2、3、3

ntile(4) : result 1、1、2、2、3、4

ntile(5) : result 1、1、2、3、4、5

ntile(6) : result 1、2、3、4、5、6

ntile(7) : result 1、2、3、4、5、6

According to the running results nitile It is sorted by groups , When the parameter is, it is sorted in groups .

Explanation 2 ：

Example

select a.Score as Score,
(select count(distinct b.Score) from Scores as b where b.Score>=a.score)as `Rank`
from Scores as a
order by a.Score desc;

Reading ：

The sub query will retrieve the total number of all scores greater than or equal to the current score , This is the rank that the score should have , Take this question as an example ：

score : 4.00 — rank :1 Greater than or equal to 4 There are two of them 4 After the weight is removed, it is 1 .

score : 4.00 — rank: 1 Greater than or equal to 4 There are two of them 4 After the weight is removed, it is 1 .

score : 3.85 — rank: 2 Greater than or equal to 3.85 There are 3 individual 4、4、3.85 After the weight is removed, it is 2 .

score : 3.65 — rank : 3 Greater than or equal to 3.65 There are 5 individual 4、4、3.85、3.65、3.65 After the weight is removed, it is 3 .

score : 3.65 — rank : 3 Greater than or equal to 3.65 There are 5 individual 4、4、3.85、3.65、3.65 After the weight is removed, it is 3 .

score : 3.50 — rank : 4 Greater than or equal to 3.65 There are 5 individual 4、4、3.85、3.65、3.65、3.50 After the weight is removed, it is 4 .