very close .. @fields is an array of hash refs, so you have to dereference it as a hash with the % ...

for ( 0 .. $#fields) {
   %sql_data = %{$fields[$_]};
  ... insert into DB ...
}
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or really just (more 'perlish' loop):

foreach my $sql_data ( @fields ) {
   $stmt = qq/INSERT INTO temp_sheet (/ . join(',', keys %$sql_data ) 
+. qq/) 
               VALUES (/ . join(',', ('?') x keys %$sql_data ) . qq/)/
+;   
   $dbh->do( $sql, {}, values %$sql_data );
}
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A quick aside -- an example using SQL::Abstract:

use SQL::Abstract;
my $sql = SQL::Abstract->new;
foreach my $data (@fields){
  my($stmt, @bind) = $sql->insert('temp_sheet', $data);
  $dbh->do( $stmt, {}, @bind );
}
[download]