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From:Joerg Bruehe Date:October 1 2010 8:59pm
Subject:Re: Not to show until a certain date
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Hi Hank, all!


Hank wrote:
> On Fri, Oct 1, 2010 at 2:34 PM, Joerg Bruehe <joerg.bruehe@stripped> wrote:
>> Hi!
>>
>>
>> Hank wrote:
>>> On Wed, Sep 29, 2010 at 8:33 AM, Patrice Olivier-Wilson
>>> <biz@stripped> wrote:
>>>> On 9/28/10 8:33 PM, Chris W wrote:
>>>>
>>>>> SELECT *
>>>>> FROM announcements
>>>>> WHERE announcements_expiredate > CURDATE()
>>>>> AND announcements_postdate <= CURDATE()
>>>>> ORDER BY announcements_expiredate ASC
>>> Or how about something like this:
>>>
>>> SELECT *
>>> FROM announcements
>>> WHERE  CURDATE() between announcements_postdate and announcements_expiredate
>>> ORDER BY announcements_expiredate ASC
>> The syntax is correct, but I don't think this statement will be
>> optimized as well as the other proposal:
>> BETWEEN is intended for "column BETWEEN const1 AND const2",
>> whereas your statement is "const BETWEEN column1 AND column2".
>>
> 
> But that only really matters if there are indexes on the column1 and
> column2 fields.

Correct.
But given that the typical question here is "how can I make it faster?"
and the typical answer "create proper indexes", we should assume there
are (or will be) indexes defined.

> 
> And for the optimizer, wouldn't it make sense to map BETWEEN into two
> comparison statements "(column>const1 and column<=const2)"  or
> "(const>column1 and const<=column2)" where both scenarios the
> optimizer may be able to use indexes on the fields?  It's exactly the
> same as the other proposal:
> 
> "CURDATE() > announcements_postdate and CURDATE()<=
> announcements_expiredate" which still is using two different fields
> for the comparisons... so wouldn't both scenarios end up in the exact
> same place?

As I wrote: Your syntax is correct. I should have added: And the
semantics are correct, too. Your approach is perfectly valid.

However, there several discussions about the optimizer at various lists
and forums which mostly agree that it might handle some constructs even
better. I don't have expert knowledge there, I can't tell what the
optimizer will do with the two statements proposed, I just fear it might
not handle "const BETWEEN column1 AND column2" as clever as you hope.


Regards,
Jörg

-- 
Joerg Bruehe,  MySQL Build Team,  joerg.bruehe@stripped
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Thread
Not to show until a certain datePatrice Olivier-Wilson28 Sep
  • Re: Not to show until a certain datePatrice Olivier-Wilson28 Sep
    • Re: Not to show until a certain dateChris W29 Sep
      • Re: Not to show until a certain datePatrice Olivier-Wilson29 Sep
        • Re: Not to show until a certain dateHank29 Sep
          • Re: Not to show until a certain dateJoerg Bruehe1 Oct
            • Re: Not to show until a certain dateHank1 Oct
              • RE: Not to show until a certain dateBMBasal1 Oct
                • Re: Not to show until a certain dateHank2 Oct
              • Re: Not to show until a certain dateJoerg Bruehe1 Oct