<?php
$db = mysqli_connect("localhost", "root", "", "ogloszenia");
?>


<form>
    <select name="user">
        <option disabled value="" selected>Wybierz uzytkownika</option>

<?php
$query = "SELECT * FROM uzytkownik";
$users = mysqli_query($db, $query);

while($row = mysqli_fetch_array($users)) {
    echo '<option value="'.$row["id"].'">'.$row["imie"].' '.$row["nazwisko"].'</option>';
}
?>

</select>
<input type="submit"></form>


<?php
if (isset($_GET["user"]) && $_GET["user"]) {
    $userId = $_GET["user"];
    $query = "SELECT * FROM ogloszenie WHERE uzytkownik_id = ".$userId;
    $dane = mysqli_query($db, $query);
    while($row = mysqli_fetch_array($dane)) {
        echo $row["tytul"]."<br>";
    }
}
    mysqli_close($db);
?>