RE: SQL Tunning

From: Goulet, Dick <DGoulet_at_vicr.com>
Date: Tue, 3 Aug 2004 12:30:08 -0400
Message-ID: <4001DEAF7DF9BD498B58B45051FBEA6506D9FD@25exch1.vicorpower.vicr.com>

Wes,

Dates are "funny" data types. They contain both the date & time which = is where your getting messed up. Trunc(sysdate) returns the sysdate, = but with time zeroed out or "04-AUG-04 00:00:00". = Trunc(sysdate)-22/86400 is returning the truncated date with 22 seconds = subtracted or "03-AUG-04 23:59:38". Now using trunc(last_update_date) = in your where clause is crippling your index, therefore using the = "last_update_date between trunc(sysdate-1) and trunc(sysdate)" is better = since you don't have to apply a function to your data one row at a time. = Your asking Oracle to determine if the date is >=3D "03-AUG-04 = 00:00:00" and <=3D "04-AUG-04 00:00:00". Dividing dates just makes no = sense at all, like a divide by 0.

Dick Goulet
Senior Oracle DBA
Oracle Certified 8i DBA

-----Original Message-----
From: Wes Brooks [mailto:wes_brooks_at_yahoo.com] Sent: Tuesday, August 03, 2004 11:54 AM
To: oracle-l_at_freelists.org
Subject: Re: SQL Tunning

Hello expert,

Thank you very much for all of your reply.

But in my case, the 1 is variable. I tried the following but it = complains that=20

SELECT TRUNC(SYSDATE)-22/86400 from dual;

TRUNC(SYS

02-AUG-04 <--- Wrong date.

SELECT TRUNC(SYSDATE-22)/86400 from dual; SELECT (TRUNC(SYSDATE)-22)/86400 from dual;

These two SQL statements gave the error:

ORA-00932: inconsistent datatypes

If I try this one, it works.

SELECT TRUNC(SYSDATE - 22), TO_DATE(TO_CHAR(TRUNC(SYSDATE-22+1), = 'DD-MON-YYYY HH24:MI:SS'),
'DD-MON-YYYY HH24:MI:SS') from dual;

Is there any way to improve this lengthly statement?

Thanks,
Wes

Edgar Chupit <edgar.chupit_at_rs.lv> wrote:

> Hello Wes,

>=20

> WB> WHERE TRUNC(last_update_date) =3D TRUNC(SYSDATE - 1)
> WB> How to improve the performance? Do I need to create a new index =
field on the table with
> TRUNC(last_update_date)?

>=20

> You have several opportunities:
> a) you can rewrite your query to this:
> where last_update_date between trunc(sysdate)-1 and =
trunc(sysdate)-1/86400
> b) you can create function based index like:
> create index tt_idx on tt(trunc(last_update_date));
> c) you can add column to your table with values from =
trunc(last_update_date)
>=20
> What option to choose mostly depends on your requirements.

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Received on Tue Aug 03 2004 - 11:26:09 CDT