MySQL取离当前时间最近的记录

sql获取当前时间：NOW()， sql获取当前日期：DATE( CURDATE( ) )

SELECT
	a.id,	
	a.start_time,
	a.end_time,
	a.in_time,
	a.out_time,
	ABS(NOW() - a.start_time) aa, 
	ABS(NOW() - a.end_time) bb,
	IF(ABS(NOW() - a.start_time) > ABS(NOW() - a.end_time), ABS(NOW() - a.end_time), ABS(NOW() - a.start_time)) AS stTime
FROM
	appointment a 
WHERE
	a.out_time IS NULL 
	AND a.start_time >= DATE( CURDATE( ) ) 
    AND a.start_time <= CONCAT( DATE( CURDATE( ) ), ' 23:59:59' )
ORDER BY stTime DESC