title: Mysqli_query returns false and Mysqli_error returns NULL?
body: <p>I've been creating a booking system, and creating appointments, but my SQL statement is not working. I've been trying to find a solution but to no avail.</p>
  
  <p>Listed below is my php code. My first SQL statement works perfectly and returns the correct ClientID, however, the second SQL statement does not insert it all into the database. I have done var_dumps on result, returning bool(false), as well as mysqli_error on the result, returning null.
  My error message at the end only displays the echo'd message, and not the mysqli_error or error number also.</p>
  
  <p>(Note: some values are changed/removed to protect data)</p>
  
  <pre><code>&lt;?php
      session_start();
      if(! $_SESSION['Username']) {
          header("location:Index.php");
      }    
      $servername = "localhost";
      $username = "root";
      $password = "";
      $dbname = "";
      $tablename = "appointmentinformation";
      $tablenamed = "clientinformation";
  
      $connection = mysqli_connect("$servername", "$username", "$password", "$dbname") or die("Could not connect to the database");
  
      $clientusername = $_SESSION['Username'];
      $sql = "SELECT ClientID FROM $tablenamed WHERE Username = '$clientusername' LIMIT 1";
      $results = mysqli_query($connection, $sql);
      if (! $results) {
          echo ("Could not select the data : " . mysql_error());
      } else {
          $datarows = mysqli_fetch_row($results);
          $clientid = $datarows[0];
      }
  
      $date = $_POST["Date"];
      $month = $_POST["Month"];
      $year = $_POST["Year"];
      $time = $_POST["Time"];
      $length = $_POST["Length"];
  
      $date = stripslashes($date);
      $month = stripslashes($month);
      $year = stripslashes($year);
      $time = stripslashes($time);
      $length = stripslashes($length);
  
      $date = mysqli_real_escape_string($date);
      $month = mysqli_real_escape_string($month);
      $year = mysqli_real_escape_string($year);
      $time = mysqli_real_escape_string($time);
      $length = mysqli_real_escape_string($length);
  
      $query = "INSERT INTO appointmentinformation (ClientID, Length, Date, Month, Year, Time, Price) VALUES ('$clientid', '$length', '$date', '$month', '$year', '$time', '$price')";
      $result = mysqli_query($connection, $query);
      if ($result) {
          header("Location:UserCP.php");
      } else {
          echo ("Could not insert data : " . mysqli_error($result) . " " . mysqli_errno());
      }
  ?&gt;
  </code></pre>