foreach (@fields) {
   
  my $sth = $dbh->prepare( 'INSERT INTO temp_sheet ('
                           .join(',', keys %$_)
                           .') VALUES ('.
                           .join(',', map {'?'} keys %$_)
                           .')'
                          );
  
  $sth->execute(values %$_);
}

##</code><code>##

# list your headers
my @heading = qw[description billing_code user_id 
                 project_id bad_proj bad_bill bad_user];

# now prepare a statement *once*
my $sth = $dbh-<prepare('INSERT INTO temp_sheet ('
                        .join(',', @heading)
                        .') VALUES ('.
                        .join(',', map {'?'} @heading)
                        .')'
                       );

# now insert
foreach my $row (@fields) {
   $sth->execute( map { $row{$_} } @heading );
}

##</code><code>##

my @heading;
{
   my $sth = $dbh->prepare('SELECT TOP 1 * FROM temp_sheet');
   $sth->execute;
   @heading = @{ $sth->{NAME_lc} };
}