我尝试将两个表连接在一起，然后使用api以json格式检索数据。
当我在phpmyadmin中加入表时，它工作得很好，但是当我在php代码中使用完全相同的sql语句并使用postman对其进行测试时，不会返回任何结果。
请帮帮我，
非常感谢，

PHP CODE:

$app->get('/api/getbooking', function(Request $request, Response $response){
     session_id('TEST'); // NEED TO FIND A WAY TO CARRY SESSIONS OVER SUBDOMAINS - ASSIGNING THE ID IS BAD!
     session_start();
    //$sql = "Select * from login where username ='{$_SESSION['Username']}'";

     $sql= "SELECT *
      FROM booking 
      INNER JOIN artistlocation ON booking.ArtistID = artistlocation.ArtistID
      WHERE CustomerID = 13";

    try{
        $db = new db();
        $db = $db->connect();

        $stmt = $db->query($sql);
        $customers = $stmt->fetchAll(PDO::FETCH_OBJ);

        $db = null;
        echo json_encode($customers);

        //This whole block of code needs improving
    }
    catch(PDOException $e){
        echo '{"error": {"text": '.$e->getMessage().'}';
    }
});