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Problem solution · SQL

League Statistics

League Statistics: a SQL solution using relational aggregation. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Relational aggregation
Source
walkccc LeetCode Solutions
Length
45 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Relational aggregation

For League Statistics, the query transforms and combines relational rows, then filters or aggregates them into the requested result.

  1. Identify the source rows and join keys.
  2. Apply filters before aggregation when possible.
  3. Group, rank, or project the final columns required by the result.

Code notes

  • 45 lines of SQL from the credited upstream file 1841.sql.
  • The implementation keeps its working state in language-native values and containers.
  • No explicit loop blocks detected.

Complexity

Review join cardinality, grouping keys, and available indexes when estimating query cost.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeLeague Statistics · SQLSQL
Use this to learn the idea, then write your own version.
SELECT  Teams.team_name,  SUM(    CASE      WHEN Matches.home_team_id = Teams.team_id      OR Matches.away_team_id = Teams.team_id THEN 1      ELSE 0    END  ) AS matches_played,  SUM(    CASE      WHEN Teams.team_id = Matches.home_team_id      AND Matches.home_team_goals > Matches.away_team_goals THEN 3      WHEN Teams.team_id = Matches.away_team_id      AND Matches.home_team_goals < Matches.away_team_goals THEN 3      WHEN Matches.home_team_goals = Matches.away_team_goals THEN 1      ELSE 0    END  ) AS points,  SUM(    CASE      WHEN Matches.home_team_id = Teams.team_id THEN Matches.home_team_goals      ELSE Matches.away_team_goals    END  ) AS goal_for,  SUM(    CASE      WHEN Matches.home_team_id = Teams.team_id THEN Matches.away_team_goals      ELSE Matches.home_team_goals    END  ) AS goal_against,  SUM(    CASE      WHEN Matches.home_team_id = Teams.team_id THEN Matches.home_team_goals - Matches.away_team_goals      ELSE Matches.away_team_goals - Matches.home_team_goals    END  ) AS goal_diffFROM MatchesINNER JOIN Teams  ON (    Matches.home_team_id = Teams.team_id    OR Matches.away_team_id = Teams.team_id)GROUP BY 1ORDER BY points DESC, goal_diff DESC, team_name;

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