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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