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From:Johan De Meersman Date:August 31 2011 11:24am
Subject:Re: utility of an index
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----- Original Message -----
> From: "Dave Dyer" <ddyer=mysql@stripped>
> 
> It depends on if you want the forest or the trees.  A frequently
> executed query asks for just the robots.  An index is an efficient way to
> select 6 of 20,000. As for why the rest are null, null is just a a
> random everything else value, left over from before the "is_robot" column
> was added.
> 
> Is there a better way to mark a small number of "special" records in
> a big data set?

No, you're doing it the right way, and the index is used exactly for what it's intended.

The NULL is out of place, though - is_robot sounds (and probably is) binary; use it as
such and set all the NULLs to 0 instead. NULL means "I really, honestly don't know, there
simply is no value for this field". In this case, there is a value: "no, it's not a
robot".

You may never run into problems with it, or you could slam headfirst into weirdness at
some point - NULL has some very peculiar properties that are best avoided if you don't
need them.



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Thread
Re: utility of an indexDave Dyer30 Aug
Re: utility of an indexJohan De Meersman31 Aug