$month=`date --date='1 month ago' +%B`;
my $sth = $dbh->prepare("SELECT * from $table where monthname(Date)='$month'" );
##</code><code>##

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\alex>date --date='1 month ago' +%B
The system cannot accept the date entered.
Enter the new date: (dd-mm-yy)

##</code><code>##

my $month=(localtime())[4]+1;
...
my $sth=$dbh->prepare("SELECT * from $table where month(Date)=?");
$sth->execute($month);
...

##</code><code>##

my $month=(localtime())[4]+1;
# last month:
$month--; 
$month||=12;
...
my $sth=$dbh->prepare("SELECT * from $table where month(Date)=?");
$sth->execute($month);
...

##</code><code>##

my $lastmonth=(localtime())[4]||12;
...
my $sth=$dbh->prepare("SELECT * from $table where month(Date)=?");
$sth->execute($lastmonth);
...

##</code><code>##

...
my $sth=$dbh->prepare('SELECT * from '.$dbh->quote_identifier($table).' where month(Date)=?');
...