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

try this one

select * from
  (SELECT id, name, department, age, score,
  ROW_NUMBER() OVER (partition by department order by age desc, score asc) srlno 
  FROM student) 
where srlno = 1;

Answer 2

In addition to Allan's answer, this works fine too:

select * 
from (SELECT * 
  FROM student
  order by age asc, 
           score desc) 
where rownum = 1;

Answer 3

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).

Answer 4

select to_char(job_trigger_time,'mm-dd-yyyy') ,job_status from
(select * from kdyer.job_instances ji INNER JOIN kdyer.job_param_values pm 
on((ji.job_id = pm.job_id) and (ji.job_spec_id = '10003') and (pm.param_value='21692') )
order by ji.job_trigger_time desc)
where rownum<'2'