Consulta SQL para intervalos de tempo. Erros de sintaxe.

SELECT r.user_id, r.reading_time start_time, rm.reading_time end_time, 
       (CONVERT(varchar(10), r.x)+' ; '+CONVERT(varchar(10), r.y)) start_point, 
       (CONVERT(varchar(10), rm.x)+' ; '+CONVERT(varchar(10), rm.y)) end_point 
FROM Readings r 
OUTER APPLY (SELECT TOP 1 r2.user_id, r2.reading_time, r2.x, r2.y
             FROM Readings r2
             WHERE r2.user_id=r.user_id and 
                   r2.reading_time < r.reading_time
             ORDER BY r2.reading_time desc) rm 
ORDER BY 1,2 desc;