Re: proposal : cross-column stats

2010/12/13 Josh Berkus <josh(at)agliodbs(dot)com>:
> Tomas,
>
>>   (a) find out what statistics do we need to collect and how to use it
>>   (b) implement a really stupid inefficient solution
>>   (c) optimize in iterations, i.e. making it faster, consuming less
>>       space etc.
>
> I'll suggest again how to decide *which* columns to cross: whichever
> columns are combined in composite indexes.  In version 2, allow the DBA
> to specify combinations.

It's really good idea? Composite index can be created when single
columns are too less unique - (name, surname). DBA specification can
be cheeper. We can set a options for relation? So it can be used.

Pavel

>
> In the unlikely event that correlation could be reduced to a single
> float number, it would be conceivable for each column to have an array
> of correlation stats for every other column where correlation was
> non-random; on most tables (i.e. ones with less than 100 columns) we're
> not talking about that much storage space.
>
> The main cost would be the time spent collecting that info ...
>
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