Do you have any records in that date range ?. Check with this

#!/usr/bin/perl
use DBI;
use strict;

my $sql =<< "SQL";
  SELECT YEAR(DAT_END),MONTH(DAT_END),COUNT(*)
  FROM session
  GROUP BY YEAR(DAT_END),MONTH(DAT_END)
SQL

my $dbh = get_dbh();
my $ar  = $dbh->selectall_arrayref($sql);
print "YEAR\tMONTH\tCOUNT\n";
for (@$ar){
  print join "\t",@$_,"\n;
};
$dbh->disconnect;
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