How Do I add a record to a table if it dont exist ??

[FLAHERTY, JIM-CONT]

I have a delima I want to add records to a table in mysql , only if that
record isnt there , Help 
 
 
Code 
 
my $sth1 = $dbh -> prepare("select distinct testname from testhistory");
$sth1 -> execute or die " unable to execute query ";
#$sth1 -> finish;
 
my $array_ref1 = $sth1->fetchall_arrayref();
 

  foreach $row(@$array_ref1) {
     my($tname) = @$row;
 

    my $sth5 = $dbh-> prepare("select testname from phistory");
    $sth5 -> execute or die " unable to execute query ";
    #$sth1 -> finish;
 
     my $array_ref5 = $sth5->fetchall_arrayref();
        foreach $row1(@$array_ref5) {
           my($tname) = @$row1;
 
    if ($tname ne ""){
 my $sth2 = $dbh -> prepare("insert into
phistory(testname)values('$tname')");
$sth2 -> execute or die " unable to execute query ";
#$sth1 -> finish;
 
}
 
}
 
 
this code doesnt add at all 
Thanks 
Jim