How to Select the Top 10 Oracle Records While Excluding Specific Dates?

Oracle Top 10 Record Selection with Date Exclusion

This article addresses the common Oracle database challenge: retrieving the top 10 records ordered by a specific column, while simultaneously excluding records matching specific criteria from another table. A simple SELECT DISTINCT with an ORDER BY and ROWNUM clause won't suffice due to the interaction of these elements.

The solution utilizes a subquery to achieve the desired outcome:

SELECT *
FROM (
  SELECT DISTINCT 
  APP_ID, 
  NAME, 
  STORAGE_GB, 
  HISTORY_CREATED, 
  TO_CHAR(HISTORY_DATE, 'DD.MM.YYYY') AS HISTORY_DATE  
  FROM HISTORY 
  WHERE 
    STORAGE_GB IS NOT NULL 
    AND NOT EXISTS (
      SELECT 1
      FROM HISTORY h2
      WHERE 
        h2.APP_ID = HISTORY.APP_ID
        AND TO_CHAR(h2.HISTORY_DATE, 'DD.MM.YYYY') ='06.02.2009'
    )
  ORDER BY STORAGE_GB DESC
)
WHERE 
  ROWNUM <= 10;

This approach first filters the HISTORY table within the inner query. The NOT EXISTS clause efficiently excludes records where APP_ID matches records with HISTORY_DATE equal to '06.02.2009'. The results are then ordered by STORAGE_GB (descending). The outer query applies the ROWNUM <= 10 constraint, ensuring only the top 10 records are returned. This method correctly applies the row limit after the filtering and ordering, guaranteeing accurate results.

Note: NOT EXISTS generally offers better performance than NOT IN for this type of exclusion, particularly with large datasets. Consult Oracle documentation for further performance optimization strategies.

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