NYCPHP Meetup

[Daniel Convissor]

On Sat, Sep 27, 2008 at 08:54:10PM -0400, Michael B Allen wrote:
> 
> So is the first column of a primary key always also an index? I
> thought I read somewhere that the columns are concatenated together to
> form one index?

I don't think they're actually concatenated.  The manual says:

   A multiple-column index can be _considered_ a sorted array
   containing values that are created by concatenating the values
   of the indexed columns.

Emphasis on "considered" is mine.  However MySQL stores it, the engine 
has the ability to utilize it.  More information (and the quote above) 
are from 
http://dev.mysql.com/doc/refman/5.0/en/multiple-column-indexes.html

--Dan

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