INSERT INTO table SET ip = INET_ATON('173.194.67.94')

SELECT INET_NTOA(ip) FROM table

if (
 (!empty($bnetname))
 &&
 ($name="validate")
 &&
 ($alreadyinDB==0)
)

display_errors = on  
error_reporting = E_all & ~E_notice

 $checkip = $db->query("SELECT * FROM participants WHERE ip LIKE '$ip'");

if ((!empty($bnetname))&&($name="validate")&&(empty($checkip)))
{ etc....}

....
$checkip = $db->query("SELECT * FROM participants WHERE ip LIKE '$ip'");
    $alreadyinDB=0;
    foreach($checkip as $row)
    {
      $alreadyinDB=1;
    }

.....

//Execute INSERT statement if a name has been filled in
    if ((!empty($bnetname))&&($name="validate")&&($alreadyinDB==0)){
    $stmt->execute();
    }
    elseif ((!empty($bnetname))&&($name="validate")&&($alreadyinDB==1)){
    print "Only 1 entry per IP is allowed";
    }

<?php
$bnetname = $_POST['bnetname'];
$ip = $_SERVER['REMOTE_ADDR']; 

try
  {
    
    //open the database
    $db = new PDO('sqlite:bnetnames.sqlite');

    //create the database
    $db->exec("CREATE TABLE participants (Id INTEGER PRIMARY KEY, bnetname TEXT, ip INTEGER)");     
    
    // check if an IP adress already is in the table, if it is not then execute the prepared INSERT statement 
    $checkip = $db->query("SELECT * FROM participants WHERE ip LIKE '$ip'");

    //prepare INSERT statement
    $stmt= $db->prepare("INSERT INTO participants(bnetname, ip) VALUES (:bnetname, :ip)");
    
        //bind statement variables directly to input values
    $stmt->bindParam(':bnetname', $bnetname, SQLITE3_TEXT);
    $stmt->bindParam(':ip', $ip, SQLITE3_TEXT);
    
    //Execute INSERT statement if a name has been filled in and IP is not already in db
    if ((!empty($bnetname))&&($name="validate")&&(empty($checkip)))
        {
    $stmt->execute();
    }
?>