I'm new to SQL and while I understand the basics, I'm trying to improve my skills by practicing on LeetCode. I came across the below problem and I'm trying to understand what is going on in the solution as I can't wrap my head around it:

Table: Scores

 ------------- --------- 
| Column Name | Type    |
 ------------- --------- 
| id          | int     |
| score       | decimal |
 ------------- --------- 

Problem: Write an SQL query to rank 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.

Solution:

SELECT
  Score,
  (SELECT count(distinct Score) FROM Scores WHERE Score >= s.Score) Rank
FROM Scores s
ORDER BY Score desc

What's going on in the sub-query? Could someone explain what it's doing by breaking it down? Any resources I could reference to better understand?

CodePudding user response：

The best way is to test it with different values.

In plain English, I would say that for each row R1 in Scores table we count the number of scores having a larger value than R1.score (plus one).

CodePudding user response：

I believe this is what you want, if not, I'm sorry:

SELECT
    s.Score --field [score] in each row from table Scores
    , (
        SELECT
            count(distinct s.Score) --counting only unique (distinct) values that are bigger than field [score] from current row outside subquery
        FROM
            Scores
        WHERE
            Score >= s.Score --filtering only rows with field [score] bigger than field [score] from current row outside subquery
    ) Rank --alias from field created by subquery
FROM
    Scores s --Query all rows in table Scores
ORDER BY
    Score desc --sort rows by score from bigger to smaller