TOP-N Schema List

SELECT owner, wsize  "Size in MB"
  FROM ( SELECT owner, sum(bytes/(1024*1024)) wsize, RANK() OVER (ORDER BY sum(bytes/(1024*1024)) DESC) sal_rank
           FROM dba_segments group by owner)
 WHERE sal_rank <= 5;

 SELECT owner, wsize  "Size in MB"
  FROM ( SELECT owner, sum(bytes/(1024*1024)) wsize, DENSE_RANK() OVER (ORDER BY sum(bytes/(1024*1024)) DESC) sal_rank
           FROM dba_segments group by owner)
 WHERE sal_rank <= 5;