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sandro

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Since: Mar 27, 2009
Posts: 1



(Msg. 1) Posted: Fri Mar 27, 2009 11:25 am
Post subject: index for bitwise comparison?
Archived from groups: comp>databases>mysql (more info?)
Hi,

is it any possible/usefull to add an index for bitwise comparison
(e.g.: ti2.t_m3 & 134217728). I don't think so but I'm not totally
sure.

Thanks
sandro

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toby

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Since: Aug 21, 2008
Posts: 6



(Msg. 2) Posted: Fri Mar 27, 2009 6:53 pm
Post subject: Re: index for bitwise comparison? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
On Mar 27, 10:58 am, sandro wrote:
> Hi,
>
>    is it any possible/usefull to add an index for bitwise comparison
>   (e.g.:  ti2.t_m3 & 134217728). I don't think so but I'm not totally
>   sure.
>
>   Thanks
>   sandro

No. But splitting the mask into individual indexed columns may help
you.

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toby

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Since: Aug 21, 2008
Posts: 6



(Msg. 3) Posted: Sat Mar 28, 2009 6:21 am
Post subject: Re: index for bitwise comparison? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
On Mar 27, 10:58 am, sandro wrote:
> Hi,
>
>    is it any possible/usefull to add an index for bitwise comparison
>   (e.g.:  ti2.t_m3 & 134217728). I don't think so but I'm not totally
>   sure.

An ordinary BTree index can help you narrow down the search if you
know the leading bits. For example, if your keys are 8 bits, values
matching
0,1,0,X,X,X,X,X
can be extracted by
key BETWEEN 64 AND (64+31)

Depending on your data and query patterns it may be more efficient to
break the bitmask into separate indexed columns, or even normalise
further into individual relations.

>
>   Thanks
>   sandro
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