Oracle-L: Re: No Nulls? (was: Warehouse design: snowflake vs star schemas)

From: <Jared.Still_at_radisys.com>
Date: Mon, 14 Oct 2002 10:53:56 -0800
Message-ID: <F001.004E8465.20021014105356@fatcity.com>

Rich,

NULLs are one of those religious war topics.

They have a legitimate place in an RDBMS, but I think you need to be judicious in using them.

If a column is to be used as part of a where clause, I prefer to use a default value, particularly with dates.

NULLs can be a real performance killer when used this way.

Here's an example where a begin date is known, the end date may be specifed or not. If not, it is NULL.

NULL: select *
from mytab
where begin_date >= to_date('06/18/2001','mm/dd/yyyy') and (

end_date <= ' to_date('08/30/2001','mm/dd/yyyy') or
end_date is NULL
)

The problem with that one is obvious. The SQL is a little convoluted and it's going to be slow due to the NULL.

DEFAULT VALUE of 12/31/4712 for unknown or unspecified end_date:

select *
from mytab
where begin_date >= to_date('06/18/2001','mm/dd/yyyy') and (

end_date <= ' to_date('08/30/2001','mm/dd/yyyy') or
end_date = to_date('12/31/4712','mm/dd/yyyy') )

Jared

"Jesse, Rich" <Rich.Jesse_at_qtiworld.com>
Sent by: root_at_fatcity.com
10/14/2002 10:33 AM
Please respond to ORACLE-L

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
        cc: 
        Subject:        No Nulls? (was: Warehouse design: snowflake vs star schemas)

On the link below is this quote from C.J.Date:

"I don't want you to think that my SQL solution to your problem means I advocate the use of nulls. Nulls are a disaster."

Of course, he doesn't expound upon it (probably not a need except for dummies like me). Anyone care to comment? (On the quote, not on my dumminess...)

Rich

Rich Jesse                           System/Database Administrator
Rich.Jesse_at_qtiworld.com              Quad/Tech International, Sussex, WI

USA
> -----Original Message-----
> From: Robson, Peter [mailto:pgro_at_bgs.ac.uk]
> Sent: Monday, October 14, 2002 4:59 AM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: Warehouse design: snowflake vs star schemas
>
>
> Just for the record (and perhaps to confirm that there are
> always two sides
> to a story). Readers may like to see the article Chris Date
> wrote to Ralph
> Kemball on the subject of business rules and integrity constraints:
>
> http://www.dbdebunk.com/kimball1.htm

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Jesse, Rich
  INET: Rich.Jesse_at_qtiworld.com

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).



-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: 
  INET: Jared.Still_at_radisys.com

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).

Received on Mon Oct 14 2002 - 13:53:56 CDT