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Die Top-N-Zeilen pro Gruppe auswählen snippet

Die Top-N-Zeilen innerhalb jeder Gruppe behalten — die Top 3 Verdienenden pro Abteilung, die neueste Bestellung pro Kunden.

Die Top-N-Zeilen innerhalb jeder Gruppe behalten — die Top 3 Verdienenden pro Abteilung, die neueste Bestellung pro Kunden. GROUP BY kollabiert jede Gruppe auf eine Zeile, was hier genau falsch ist: stattdessen ranken. ROW_NUMBER() OVER (PARTITION BY die Gruppe ORDER BY das Ranking) nummeriert die Zeilen innerhalb jeder Gruppe, sodass das Filtern auf den Rang exakt N pro Gruppe behält. ROW_NUMBER() gegen RANK() tauschen, wenn Zeilen mit Gleichstand beide in die Auswahl kommen sollen.

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SQLSQLrunnable
-- Top 3 earners per department: rank inside each group, keep rn <= 3.
WITH ranked AS (
  SELECT
    department,
    name,
    salary,
    ROW_NUMBER() OVER (PARTITION BY department ORDER BY salary DESC) AS rn
  FROM employees
)
SELECT department, name, salary
FROM ranked
WHERE rn <= 3
ORDER BY department, salary DESC;

Runs as-is in the playground's SQLite (window functions need SQLite 3.25+). RANK() keeps ties — two rows share rank 1 and both survive an rn <= N filter — while ROW_NUMBER() always breaks ties arbitrarily.

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