PHP question

[Mike Rambo]

I have a question for any/all PHPer's out there.

Our shop database system is up to a couple thousand entries now, and
we'd like to start getting some statistics out of it. We're tracking the
repairs we perform and the data includes, among other things, receive
and completion dates for each piece of equipment. We'd like to generate
a report that would show the average time it has taken over the last 30,
60, and 90 days to turn around each piece of equipment (ie. fix it and
get it out the door). The dates are stored in Mysql in the form
YYYY-MM-DD. I'm having some difficulty determining which is the best way
to select the data from Mysql in the first place, and then how to
manipulate it (mathematically) with PHP thereafter. I've looked at
several different things I've found on phpbuilder.com and devshed.com
but they've left me mildly confused as to what the best way might be to
accomplish this. It seems the facilities for manipulating dates in PHP
are not real refined. ASP, from what I'm told, has a diffdate() function
that would appear to help a great deal but an equivalent does not exist
in PHP4.

What I think I need:

*count number of records completed in the last X number of days
*select all records completed in the last X number of days
*determine days it took to complete each machine
*sum number of days for all machines
*divide total days by number of machines in time period

I've got code that will iterate through the records once they're
selected. My difficulty is in _how_ to do the selection and how to do
the date mathematics thereafter. It appears I can strip the '-' out of
the date once I have it out of PHP into a variable, and then ostensibly
perform some arithmetic operations on it - is this correct? Also, I'm
not sure how to tell Mysql how to select records that have a
complete_date > (current_date - 30) when the date is not stored as a
purely numeric entry.

Any insight?


-- 
Mike Rambo
mrambo@lsd.k12.mi.us