You're wanting to check out the DBI module to get your connection to the database. Here is a simple way of going about it; I'm sure you can do the differencing within the SQL, but I never did go and learn SQL functions :). So this is one way of going about it:

=for SQL Table
------------------------------------
| theIDNum | theDate    | thePrice |
------------------------------------
| ax1      | 2004-12-01 | 300.00   |
| ax2      | 2004-12-01 | 500.00   |
| ax1      | 2004-12-02 | 200.00   |
| ax1      | 2004-12-03 | 100.00   |
| ax3      | 2004-12-01 | 300.00   |
| ax2      | 2004-12-01 | 400.00   |
------------------------------------
=cut

use strict;
use DBI;

my $dbh = DBI->connect('dbi:mysql:database', 'u', 'p', {
    RaiseError => 1, AutoCommit => 1
} );

my $rows = $dbh->selectall_arrayref(
    'SELECT thePrice FROM theTable ORDER BY ' .
    'theDate DESC, thePrice LIMIT 2'
);

my $diff = abs( $rows->[0][0] - $rows->[1][0] );

printf("%s%.2f\n", 'Difference of $', $diff);

__END__

Difference of $50.00
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Sorry I didnt not correctly state the problem

This really isn't a Perl question, it's a SQL question.

SQL is a declarative language, which means you describe what you want, rather than how to get it. You've stated you want to compare things in the same table, so you'll need aliases.

from table a join table b on -- the primary key
where a.idNumber = b.idNumber
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select abs(a.price - b.price) as difference
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where a.date = (select max(Date) from table t1
      where t1.idNumber = a.idNumber)
and
     b.Date = (select max(Date) from table t2
     where t2.idNumber = b.idNumber)
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select
      a.idNumber              -- Presuming you want
    , b.idNumber              --    these too.
    , abs(a.Price - b.Price)  -- the price difference
from
    table a join table b on SOMETHING -- the primary key
where
        a.idNumber = b.idNumber
    and a.date = (select max(Date) from table t1
         where t1.idNumber = a.idNumber)
    and b.Date = (select max(Date) from table t2
         where t2.idNumber = b.idNumber)
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Thanks alot i made a bit of a work around but got that to work. I have a futher SQL problem but i will address that in a more appropriate area, thanks again