Question

What i am trying to do is a simple recommender , must take the biggest weighted top 40 element’s node2 element. Calculation for weight comes from (E.WEIGHT * K.GRADE). Now this code succesfully returns top 40 elements. However, i don’t want E.NODE2 to return duplicates. POSTGRE SQL allowed me to do SELECT DISTINCT ON (NODE2) E.NODE2 , (E.WEIGHT * K.GRADE). How can i do the same in oracle?

The complete sql query;

SELECT *
 FROM   (SELECT DISTINCT E.NODE2  , (E.WEIGHT * K.GRADE)
    FROM KUAISFAST K, EDGES E
    WHERE K.ID = 1 AND K.COURSE_ID = E.NODE1 AND E.NODE2 NOT IN(
        SELECT K2.COURSE_ID
        FROM KUAISFAST K2
        WHERE K2.ID = 1
        ) 
    ORDER BY( E.WEIGHT * K.GRADE ) DESC) TEMP
WHERE rownum <= 40

Answer 1

This should solve your problem, altough quite slow

SELECT * FROM
(SELECT *
 FROM   (SELECT E.NODE2 ,  max(E.WEIGHT * K.GRADE ) AS MAXDE
    FROM KUAISFAST K, EDGES E
    WHERE K.ID = 1 AND K.COURSE_ID = E.NODE1 AND E.NODE2 NOT IN(
        SELECT K2.COURSE_ID
        FROM KUAISFAST K2
        WHERE K2.ID = 1
        ) 
        GROUP BY E.NODE2 )
ORDER BY MAXDE DESC)
WHERE rownum <= 40