Welcome to Subscribe On Youtube

178. Rank Scores

Description

Table: Scores

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| score       | decimal |
+-------------+---------+
id is the primary key (column with unique values) for this table.
Each row of this table contains the score of a game. Score is a floating point value with two decimal places.

 

Write a solution to find the rank of the scores. The ranking should be calculated according to the following rules:

• The scores should be ranked from the highest to the lowest.
• If there is a tie between two scores, both should have the same ranking.
• After a tie, the next ranking number should be the next consecutive integer value. In other words, there should be no holes between ranks.

Return the result table ordered by score in descending order.

The result format is in the following example.

 

Example 1:

Input: 
Scores table:
+----+-------+
| id | score |
+----+-------+
| 1  | 3.50  |
| 2  | 3.65  |
| 3  | 4.00  |
| 4  | 3.85  |
| 5  | 4.00  |
| 6  | 3.65  |
+----+-------+
Output: 
+-------+------+
| score | rank |
+-------+------+
| 4.00  | 1    |
| 4.00  | 1    |
| 3.85  | 2    |
| 3.65  | 3    |
| 3.65  | 3    |
| 3.50  | 4    |
+-------+------+

Solutions

Solution 1: Direct Implementation

Use the DENSE_RANK() function, the syntax is as follows:

DENSE_RANK() OVER (
    PARTITION BY <expression>[{,<expression>...}]
    ORDER BY <expression> [ASC|DESC], [{,<expression>...}]
)

In this syntax:

• First, the PARTITION BY clause divides the result set generated by the FROM clause into partitions. The DENSE_RANK() function is applied to each partition.
• Second, the ORDER BY clause specifies the order of rows in each partition that the DENSE_RANK() function operates on.

Unlike the RANK() function, the DENSE_RANK() function always returns consecutive ranking values.

Solution 2

MySQL 8 has only provided ROW_NUMBER(), RANK(), DENSE_RANK() and other [window functions] (https://dev.mysql.com/doc/refman/8.0/en/window-function-descriptions.html)，在之前的版本，可以使用变量实现类似的功能。

• Python
• SQL

• import pandas as pd
  
  
  def order_scores(scores: pd.DataFrame) -> pd.DataFrame:
      # Use the rank method to assign ranks to the scores in descending order with no gaps
      scores["rank"] = scores["score"].rank(method="dense", ascending=False)
  
      # Drop id column & Sort the DataFrame by score in descending order
      result_df = scores.drop("id", axis=1).sort_values(by="score", ascending=False)
  
      return result_df
  
  

• # Write your MySQL query statement below
  SELECT
      score,
      DENSE_RANK() OVER (ORDER BY score DESC) AS 'rank'
  FROM Scores;
  
  
  -- Solution 2
  SELECT
      Score,
      CONVERT(rk, SIGNED) `Rank`
  FROM
      (
          SELECT
              Score,
              IF(@latest = Score, @rank, @rank := @rank + 1) rk,
              @latest := Score
          FROM
              Scores,
              (
                  SELECT
                      @rank := 0,
                      @latest := NULL
              ) tmp
          ORDER BY
              Score DESC
      ) s;
  
  

All Problems

All Solutions