Re: cheapest way to access every 15th row in table ordered by timestamp column

  • From: Niall Litchfield <niall.litchfield@xxxxxxxxx>
  • To: Chris.Stephens@xxxxxxx
  • Date: Wed, 19 Jan 2011 18:08:43 +0000

What does every 15th row mean? Would only storing every 15th sample be more

On 19 Jan 2011 16:22, "Stephens, Chris" <Chris.Stephens@xxxxxxx> wrote: on Linux 5

We have a lab instrument recording information every 2 seconds into a table.

The scientists pull that data into excel for analysis (I hope to look at
this excel spreadsheet in the very near future now that I’ve read chapter 9
of Pro Oracle SQL).

They are requesting a view that picks out every 15th row of data going back
30 days.

Can anyone think of a more efficient way to do it than this:

SELECT x.col,


      FROM ( SELECT col,


                                   rownum rn

                         FROM t

                        WHERE t_stamp >= TRUNC( SYSDATE - 30 )) x

     WHERE MOD( x.rn, 15 ) = 0;

It feels like there should be a better way to do it.


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