$comp_count = 0;
$per_count = 0;		
$SqlString = "select * from comp where ALFA = \"    \" and COMPANY = \"    \"";
$comp = $conn->query($SqlString);
while ($row_comp = $comp->fetch_array())
{
	$comp_count++;
	$comp_id = $row_comp['TID'];		
	$SqlString = "select * from pers where TID = \"$comp_id\"";
	echo "str = ".$SqlString."<br>";
	if ($pers = $conn->query($SqlString))
	{
		if ($pers->num_rows > 0)
		{
			while ($row_pers = $pers->fetch_array())
			{
				$pers_id = $row_pers['PNID'];
				$SqlString = "delete from pers where TID = '$comp_id' and PNID = '$pers_id'";
				$pers = $conn->query($SqlString);
				$per_count++;
			}
		} else {
			echo "<p>No records found for query $SqlString</p>\n";
		}
	}
	else 
	{
  		if ($conn->error) 
		{
  			echo "{$conn->error}<br>SQL = $SqlString";
	  	} 
		else 
		{
  			echo '$conn is a(n) '. gettype($conn);
  		}
	}
}

Select all