Find Players With Zero Or One Losses - Leetcode Solution

Problem Statement: You are given a table, Scores, containing two columns: 'Player' and 'Score'. The table contains data about the players and their scores in a competition. Write a SQL query to find all the players with zero or one loss. The output should be ordered by the player's ID.

Sample Input:

Scores Table:

| Player | Score | |--------|-------| | 1 | 10 | | 2 | 20 | | 3 | 30 | | 4 | 40 | | 5 | 50 | | 6 | 60 | | 7 | 70 |

Sample Output:

Output Table:

| Player | |--------| | 1 | | 2 |

Explanation: The players with the IDs of 1 and 2 have 0 or 1 losses and are therefore included in the output.

Solution:

The problem requires us to find the players with 0 or 1 loss. We can start with aggregating the number of losses by counting the number of distinct games lost by each player and filtering the players having 0 or 1 losses.

Now, the scores table only provides the score of each game played by a player. We can calculate the number of losses by comparing each player's highest score with the score of the other players. If the highest score of a player is less than the maximum score of any other player, we consider it a loss for that player.

The SQL query for the solution is given below:

SELECT Player
FROM 
    (SELECT Player, COUNT(DISTINCT b.Player) AS losses
     FROM Scores a LEFT JOIN Scores b ON a.Player != b.Player AND a.Score < b.Score
     GROUP BY Player) p
WHERE p.losses <= 1
ORDER BY Player;

Explanation:

We start by creating a subquery to count the number of losses of each player. We do this by using a self-join on the Scores table where we match each row with all the other rows having the same or higher scores.

SELECT Player, COUNT(DISTINCT b.Player) AS losses
FROM Scores a LEFT JOIN Scores b ON a.Player != b.Player AND a.Score < b.Score
GROUP BY Player

Since we are only interested in the number of other players having higher scores than a player, we use the condition a.Score < b.Score in the join statement. Also, we use the DISTINCT keyword with the count function to avoid counting the same player multiple times.

We then use this subquery as a derived table named p to filter the players having 0 or 1 losses.

WHERE p.losses <= 1

Finally, we order the result by the player's ID using the ORDER BY clause.

ORDER BY Player;

The output table will have the player IDs of the players with 0 or 1 losses, sorted in ascending order.

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