PHP函数问题PDO致命错误：未捕获的错误：在null上调用成员函数prepare（）

Question

我在第88行收到以下错误，对于我一生，我无法弄清原因。我目前正在尝试在讲话时解决问题，但也认为发帖也是一个好办法。

错误是：

  

[2019年5月10日09:42:13 UTC] PHP致命错误：未捕获错误：在C：\ inetpub \ wwwroot \ SupportDesk \ php \ Add_New_Engineer.php：88中调用成员函数prepare（）   堆栈跟踪：   0 C：\ inetpub \ wwwroot \ SupportDesk \ php \ Add_New_Engineer.php（5）：create_eng（）   1 {main}在第88行的C：\ inetpub \ wwwroot \ SupportDesk \ php \ Add_New_Engineer.php中抛出

代码：

Function create_eng(){
    global $msgID;
    global $msg, $conn;
    $msgID = 0;
    //Get POST from submit
    $eng_name = $_POST['EngineersName'];

    //SQL Query
    $sql_count = "select count(*) as num from [Engineers] where [Engineer] = :eng_name";
    //Query SQL Statement
    $stmt = $conn->prepare($sql_count);
    $stmt->bindValue(':eng_name', $eng_name);
    //Execute SQL Statement
    $stmt->execute();
    $results=$stmt->fetchAll(PDO::FETCH_ASSOC);
    //fetchAll(PDO::FETCH_ASSOC);
    If($results['num'] > 0){
        echo $msg = "Engineer $eng_name exist's in the database";
        $msgID = 1;
    }else{
        $sql_insert = "insert into [Engineers](Engineer) values '$eng_name'";
        //Prepare SQL Statement
        $stmt = $conn->Prepare($sql_insert);
        //Execute SQL Statement
        $stmt->execute();
        $results=$stmt->fetchAll(PDO::FETCH_ASSOC);
        echo $msg = "Engineer $eng_name added to the database";
        $msgID  = 2;
    }
}