my $sth = $dbh->prepare("select ... where fld1 = ? and
                                                fld2 = ? and       
                                                fld3 = ?");
      for ($i=0; $i<800; $i++0){
       ...
       $sth->execute($var2, $var2, $var4);
       ...
      }

##</code><code>##

     for ($i=0; $i<800; $i++){
       ...
      my $sql = "select ... where fld1=" . $var1 . 
                            " and fld2=" .$var2 .  
                            " and fld3=" . $var3;
      my $sth=$dbh->prepare($sql);
      $sth->execute();
       ...
     }