in reply to Re^2: Joining two files on common field
in thread Joining two files on common field

To get a better error message, change 
$sth = $dbh->prepare("SELECT * from Matrix NATURAL JOIN Inventory");

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to 
$sth = $dbh->prepare("SELECT * from Matrix NATURAL JOIN Inventory")
   or die "Cannot prepare: " . $DBI::errstr;

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In Section Seekers of Perl Wisdom