Laminas InvalidQueryException sql statement error

Questions Components & MVC
1

Hi,
I have codes like below

        $statement = $this->adapter->createStatement("SELECT UUID() as user_id");
        $result    = $statement->execute();
        $row       = $result->current();
        $user_id   = $row['user_id'];

        $this->conn = $this->adapter->getDriver()->getConnection();
        try {
            $this->conn->beginTransaction();
            $data = [
                'user_id' => $user_id,
                'email' => $user->email,
                'password' => password_hash($user->password, PASSWORD_DEFAULT, ['cost' => 10]),
                'created_at' => $user->created_at,
            ];
            $this->tableGateway->insert($data);
            $this->conn->commit();
        } catch (Exception $e) {
            $this->conn->rollback();
            throw $e;
        }

When i execute it i get an error:

Laminas\Db\Adapter\Exception\InvalidQueryException:
Statement couldn’t be produced with sql: INSERT INTO users (user_id, email, password, created_at) VALUES (?, ?, ?, ?)

When i remove the first lines it works well.

        $statement = $this->adapter->createStatement("SELECT UUID() as user_id");
        $result    = $statement->execute();
        $row       = $result->current();
        $user_id   = $row['user_id'];

Where am I doing wrong ?
Thanks.