A complicated statement will take a while to prepare as the data base will figure out its strategy for executing it. You can keep "reusing" a prepared query with different values. This way of doing it is also better than interpolating a different Perl variable into the statement for security reasons.

To make a parameter a variable, use a placeholder:
my $query = $dbh->prepare("SELECT c2.id, c2.name as 'client' 
                          FROM client c2 
                          WHERE level = ? and status = ?");

my $level = 50;
$query->execute($level,1);
$level = 60;
$query->execute($level,1);
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Understood, thanks for the explanation. In this case I will need different queries for each column, but that's useful info nonetheless.

The next step is for me to understand the best way to loop through the array and populate the next column - if I get that, I feel I can do the rest of the coding without too much more help - famous last words I know!

I would be thinking along the following lines:

use Data::Dumper;
my %hash;

my $client = "client1";
$hash{$client}{fieldA} = 12234;

#from another query:
$hash{$client}{fieldC} = 9876;

print Dumper \%hash;
__END__
$VAR1 = {
          'client1' => {
                         'fieldA' => 12234,
                         'fieldC' => 9876
                       }
        };
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To generate your output, make an array to specify the column order: my @order = qw (fieldC fieldB fieldA); Then when processing each client, cycle through the order array, if value exists for that client, put it, if not then put "" or whatever. I am just thinking that a hash representation will work out better for accumulating the data, then make the 2D array for output after the data has been collected rather than keeping each row's columns straight during the data accumulation phase.

Update: I mentioned before that there is more than one way to retrieve the data, one of those ways is as a hash. That might be of use to you...you have a bit of reading to do!

use Data::Dumper;
my %hash;

my $client = "client1";
$hash{$client}{fieldA} = 12234;

#from another query:
$hash{$client}{fieldC} = 9876;

my @order = qw (fieldC fieldB fieldA);

foreach my $client (keys %hash)
{
   print "$client";
   foreach my $field (@order)
   {
      if (exists $hash{$client}{$field})
      {
          print "\t$hash{$client}{$field}";
      }
      else
      {
         print "\tno_value";
      }  
   }
   print "\n";
}
#prints: client1 9876    no_value    12234
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