MySQL:选择所有 parent 和最近 child 的日期和任何 future child 的日期

Question

我有一个现有查询，它可以获取父记录以及所有子记录中的最大日期。子记录是调用的电话。现在，我被要求显示最近一次“过去”通话的日期以及任何 future “预定”通话的日期。

这是我现在使用的查询:

SELECT doctor.*, contact.date_scheduled
FROM doctor 
LEFT JOIN contact ON doctor.doctorID = contact.doctorID 
AND date_scheduled = (SELECT MAX(date_scheduled) FROM contact WHERE doctor.doctorID = contact.doctorID)
ORDER BY date_scheduled DESC

有人可以告诉我如何修改此查询以获取我上面描述的两个日期吗？

Answer 1

我想这就是你想要的:

SELECT d.*,
       max(case when c.date_scheduled < now() then c.date_scheduled end) as MostRecentCall,
       group_concat(case when c.date_scheduled >= now() then c.date_scheduled end) as FutureCalls
FROM doctor d left join
     contact c
     on d.doctorID =  c.doctorID
GROUP BY d.doctorId;

这会将 future 的调用日期放入列表中，以逗号分隔。

编辑:

如果您只想让医生在未来安排通话，请使用 having 子句:

SELECT d.*,
       max(case when c.date_scheduled < now() then c.date_scheduled end) as MostRecentCall,
       group_concat(case when c.date_scheduled >= now() then c.date_scheduled end) as FutureCalls
FROM doctor d left join
     contact c
     on d.doctorID =  c.doctorID
GROUP BY d.doctorId
HAVING sum(c.date_scheduled >= now()) > 0;