my (@tables, %map);
my $q = $dbh->prepare("show tables");
$q->execute or die "Error listing tables";
        
while ( my ($table) = $q->fetchrow_array ) {
    push @tables, $table;
}
$q->finish;
for my $table (@tables) {
    $q = $dbh->prepare("describe $table");
    $q->execute or die "Error describing table $table";

    while ( my $hr = $q->fetchrow_hashref ) { 
        push @{ $map{$table} }, $hr->{Field};
    }
    $q->finish;
}

##</code><code>##

my $table_name = "CDR";
my $sql = "select ".join ",", map { "sum($_)" } @{$map{$table_name}};
$sql .= " from $table_name where Date = ? and Hour like ?";