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From:Neil Tompkins Date:October 11 2011 11:30am
Subject:Re: Index question
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Just to clarify having key indexes of (a,b) or (b,a) have no difference ?

On 11 Oct 2011, at 09:36, Johan De Meersman <vegivamp@stripped> wrote:

> ----- Original Message -----
>> From: "Alex Schaft" <alexs@stripped>
>> 
>> If you have a table with columns A & B, and might do a where on A or
>> B, or an order by A, B, would single column indexes on A and B suffice
>> or would performance on the order by query be improved by an index on
>> A,B?
> 
> Depends on usage :-)
> 
> key (a, b) is good for "where a=.." or "where a=.. and b=.."
> key (b, a) is good for "where b=.." or "where b=.. and a=.."
>  (note that the sequence of a and b in the where clause is not important)
> key (a), key (b) is good for "where a=.." or "where b=.." but will only use one index
> for "where a=.. and b=..".
> 
> I think work is ongoing on having the parser use multiple indices, but I'm not sure
> where that's at.
> 
> 
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Thread
Index questionAlex Schaft11 Oct
  • Re: Index questionJohan De Meersman11 Oct
    • Re: Index questionNeil Tompkins11 Oct
      • Re: Index questionRik Wasmus11 Oct
        • Re: Index questionAlex Schaft11 Oct
          • Re: Index questionAlex Schaft11 Oct
          • Re: Index questionRik Wasmus11 Oct
            • Re: Index questionNeil Tompkins11 Oct
              • Re: Index questionRik Wasmus11 Oct
                • Re: Index questionJohan De Meersman11 Oct
                  • Re: Index questionTompkins Neil11 Oct
                    • Re: Index questionJohan De Meersman12 Oct
  • Re: Index questionArthur Fuller11 Oct