Groups > comp.databases.ms-sqlserver > #1257

Re: what's going on with datediff function?

From	"Bob Barrows" <reb01501@NOSPAMyahoo.com>
Newsgroups	comp.databases.ms-sqlserver
Subject	Re: what's going on with datediff function?
Date	2012-09-05 18:47 -0400
Organization	A noiseless patient Spider
Message-ID	<k28lut$t25$2@dont-email.me> (permalink)
References	<aa23cac7-3e4f-4b12-83da-562fbc9c5d25@m18g2000yqp.googlegroups.com> <k256h5$gq9$1@dont-email.me> <6c01faa0-f5dd-40bd-8b7a-aae1259173ae@googlegroups.com>

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rja.carnegie@gmail.com wrote:
> On Tuesday, September 4, 2012 4:25:26 PM UTC+1, Bob Barrows wrote:
>> justaguy wrote:
>>
>>> -- task: find records / rows where createddate is 8/23/2012
>>>
>>> select *
>>> from myTBL
>>> and datediff(dy,createddate,'8/23/2012') <1
>>>
>>> -- change parameter from dy to d does not help neither
>>> What's wrong?
>>>
>>> DBMS in question: MS SQL Server 2005 Express
>>>
>>> tia
>>
>> Why not simply
>>
>> WHERE CreatedDate='20120823'
>>
>> If times are being stored in CreatedDate, then it would be:
>>
>> WHERE CreatedDate >= '20120823' and CreatedDate < '20120824'
>>
>> These solutions both allow an index on CreatedDate to be used. Your
>> datediff solution forces a table scan.
>
> I haven't checked, does it?

Of course it does ... why do you need to check? The criterion is 
non-sargable.
The only way an entire table scan would be avoided is if another indexed 
field was being filtered with sargable criterion, thus allowing a subset of 
the data to be scanned

> I'm sceptical that the DATEDIFF formula defeats SQL Server's query
> optimizer,

Ok go check it then.

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Thread

what's going on with datediff function? justaguy <lichunshen84@gmail.com> - 2012-08-30 12:34 -0700
  Re: what's going on with datediff function? Gene Wirchenko <genew@ocis.net> - 2012-08-30 14:04 -0700
  Re: what's going on with datediff function? "Bob Barrows" <reb01501@NOyahooSPAM.com> - 2012-09-04 11:25 -0400
    Re: what's going on with datediff function? "Bob Barrows" <reb01501@NOSPAMyahoo.com> - 2012-09-05 18:47 -0400
      Re: what's going on with datediff function? rja.carnegie@gmail.com - 2012-09-06 15:53 -0700
        Re: what's going on with datediff function? "Bob Barrows" <reb01501@NOSPAMyahoo.com> - 2012-09-06 19:03 -0400
        Re: what's going on with datediff function? "Bob Barrows" <reb01501@NOSPAMyahoo.com> - 2012-09-06 19:09 -0400
          Re: what's going on with datediff function? Gene Wirchenko <genew@ocis.net> - 2012-09-06 17:20 -0700
    Re: what's going on with datediff function? "Bob Barrows" <reb01501@NOSPAMyahoo.com> - 2012-09-05 18:47 -0400
  Re: what's going on with datediff function? Lutz Uhlmann <news@invalid.invalid> - 2012-09-05 08:22 +0200

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