Re: Function Based Index
- From: Fergal Taheny <ftaheny@xxxxxxxxx>
- To: puravc@xxxxxxxxx
- Date: Thu, 20 Sep 2012 23:21:28 +0100
Hi Purav,
I think Mike really hit the nail on the head here where he wrote:
*delete from <table_name> where
trunc(datetime) < (trunc(sysdate) - 31) and rownum < 1000;
*
*can also be written as:*
*
delete from <table_name> where
datetime < (trunc(sysdate) - 31) and rownum < 1000;*
Even when datetime has a time component this is true; so in this particular
case you really didn't need the FBI.
Illustration below:
select sysdate from dual;
SYSDATE
-------------------------
20-SEP-12 23:02:11
select (trunc(sysdate) - 31) from dual;
(TRUNC(SYSDATE)-31)
-------------------------
20-AUG-12 00:00:00
select * from c order by 1;
DATETIME
-------------------------
19-AUG-12 00:00:01
19-AUG-12 23:59:59
20-AUG-12 00:00:00
20-AUG-12 00:00:01
select * from c where trunc(datetime) < (trunc(sysdate) - 31);
DATETIME
-------------------------
19-AUG-12 00:00:01
19-AUG-12 23:59:59
select * from c where datetime < (trunc(sysdate) - 31);
DATETIME
-------------------------
19-AUG-12 00:00:01
19-AUG-12 23:59:59
Of course if there was no trunc on the sysdate then this would no longer be
true
Regards,
Fergal
On 20 September 2012 10:52, Purav Chovatia <puravc@xxxxxxxxx> wrote:
> :)
> This column contains datetime and is a classic case of what Jonathan has
> demonstrated in his index explosion series. Because of applications'
> limitations we cannot move from storing datetime to storing only date. One
> other solution would be to have another column which contains only the date
> and index that column and then NOT index this column which stores datetime;
> but I didn't want that additional data unnecessarily. I thought FBI would
> be simple.
>
> Thanks.
>
> On Tue, Sep 18, 2012 at 5:18 PM, Tefft, Michael J <
> Michael.J.Tefft@xxxxxxxxxx> wrote:
>
> >
> >
>
>
> --
> //www.freelists.org/webpage/oracle-l
>
>
>
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