您的 GROUP BY bookslot.b_ref 正在对记录进行分组，因此您只能看到每种情况的最后一次。

Your GROUP BY bookslot.b_ref is grouping the records, so you're only seeing the last time in each case.

尝试使用

SELECT date, time, MIN(bookslot.id_timeslot)
FROM bookslot  
LEFT JOIN timeslot ON bookslot.id_timeslot = timeslot.id_timeslot   
WHERE bookslot.status = 1 
GROUP BY bookslot.b_ref  
ORDER BY bookslot.date ASC, bookslot.id_timeslot ASC LIMIT 20