query in query or what it is

oki

i am new and i have tried all the information i found all over the web..

i have 1 wordpress site att my host and a mysql db for wp (DB1)

now i have a custom member page wher i am trying to get some information frome a second database (DB2)..

i am truin too user current user id to grab only the data for that user from the second database..

here is the code

[insert_php]
$servername = "host";
$username = "user";
$password = "pass";
$dbname = "domsand_org_db_1";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
$sql = "SELECT * FROM Medlemar WHERE Medl_nr = [current user id]";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    // output data of each row
    while($row = $result->fetch_assoc()) {
  echo "Medl_nr: " . $row['Medl_nr']. " - Namn: " . $row["namn"]. " " . $row["efternamn"]. "<br>";;
    }
} else {
    echo "0 results";
}
$conn->close();

[/insert_php]

what i want is too use [current user id] thath is number 25 .. grab the date frome the the table Medlemmar in the database domsand_org_db_1

but with all test i only get array or 0 results printed—

neeed serius help pleas