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

Approximately every 15th row where each row is about two seconds apart ...

SELECT ...
from   ...
where  extract(second from tstamp) in (0,1,30,31)
/

?



>
>From: "Stephens, Chris" <Chris.Stephens_at_adm.com>
>To: ORACLE-L <oracle-l_at_freelists.org>
>Sent: Wed, 19 January, 2011 16:20:23
>Subject: cheapest way to access every 15th row in table ordered by timestamp 
>column
>
>  
>11.2.0.2 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,
>              x.t_stamp
>      FROM ( SELECT col,
>                                    t_stamp
>                                   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.
> 
>chris
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