FIRST and LAST aggregate functions only require one sort

Hi Guys and Gals,
 

This is my first post here so here goes:

 

I came across the need to use the FIRST and LAST aggregate functions.  This
is, in fact, the first time that I have remembered of their existence when
the need arose!

 

When I looked at the execution plan I saw something I didn't expect.  This
is the basic statement:

 

SELECT MIN (c1) KEEP (DENSE_RANK FIRST ORDER BY c2)

      ,MAX (c3) KEEP (DENSE_RANK LAST ORDER BY c4)

  FROM t1;

 

Now the curious thing is that the execution plan shows only one sort!
Indeed, the number of sorts remains the same no matter how may different
ORDER BY columns I use.

 

Does anybody have any idea how Oracle does it or whether it actually does
some hidden sorts that it isn't telling us about?

 

--Tony Hasler

 



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