Get the top row after order by in Oracle Subquery

Question

I have a table student(id, name, department, age, score). I want to find the youngest student who has the highest(among the youngest students) score of each department. In SQL S

Answer 1

In addition to Bharat's answer, it is possible to do this using ORDER BY in the sub-query in Oracle (as point out by Jeffrey Kemp):

SELECT *
FROM   student s1
WHERE  s1.id IN (SELECT id
                 FROM   (SELECT   id, ROWNUM AS rn
                         FROM     student s2
                         WHERE    s1.department = s2.department
                         ORDER BY age ASC, score DESC)
                 WHERE  rn = 1);

If you use this method, you may be tempted to remove the sub-query and just use rownum = 1. This would result in the incorrect result as the sort would be applied after the criteria (you'd get 1 row that was sorted, not one row from the sorted set).