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Oracle select top 10 tips

Oracle Tips by Burleson Consulting

January 1, 2011

Oracle select top 10 tips

Question:  I know that in SQL Server you can use the “select top 10” and “select top 100” SQL clause to automatically fetch the top-n rows from a table.  What is the Oracle equivalent of the “select top 10” command?

Answer: The select top 10 is a non-ANSI SQL implementation that is unique to SQL Server.  It’s always better to use a standard ANSI solution to a top rows query, but Oracle has many ways to display the top 10 and top 100 rows from a table:

select
   *
from
   (select empno, sal row_number()
    over
       (order by sal desc) rnk from emp)
where rnk <= 10;

Oracle top-n query can be satisfied in several ways:

  • Using rownum outside an in-line view
  • Using rank with over
  • Using row_number with over

Here is a review of the top-n SQL methods in Oracle:

  • Offset first n rows:  This Oracle 12c new feature offset fetch first rows only makes it easy to display the first n rows from a table
  • Top-n SQL using subselect with ROWNUM.  You can use an inline view with ROWNUM to get the top-10 rows for any SQL query, and the rownum can be used to materialize an in-line view.  Beware, this is not always a good thing, as adding the where rownum WITH clause. 
  • Top-n SQL with dense_rank and SQL ranking functions.  Oracle SQL includes ranking functions that provide support for common OLAP rankings, such as the top 10, bottom 10, top 10 percent, and bottom 10 percent.
  • Top-n SQL using the row_number functionYou can query the top 100 rows using the Oracle row_number() and “over” syntax.

 

 
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