在单个sql查询中一起使用JOIN和group

Question

我无法一起使用JOINS和group-by：我搜索了这个......但是我找不到解决方案..问题如下：

我有两个表，第一个是main_table包含字段eid ， name ， status

第二个表是带有字段fid ， eid ， last_date ， remarks和next_date后续表

第二个表用于存储客户端的后续详细信息（存储在main_table中的客户端详细信息），我希望获得具有所选日期周期（from_date到to_date）的每个客户端的最后一个后续记录，并按降序排序next_date。

我使用了以下查询但没有工作

SELECT * 
FROM main_table as MT 
JOIN followups as MF on MT.eid=MF.eid 
WHERE MT.status='open' AND MF.NDate<='2012-12-07' 
GROUP BY MF.eid 
ORDER BY MF.next_date DESC

提前谢谢......伙计们

Answer 1

你可以尝试这样的事情：

select m.eid,
  m.name,
  m.status,
  f1.last_date,
  f1.remarks,
  f1.next_date
from maintable m
left join
(
  select max(last_date) maxLast, eid
  from followups
  where last_date between from_date and to_date
  group by eid
) f
  on m.eid = f.eid
left join followups f1
  on f.maxLast = f1.last_date
  and f.eid = f1.eid
where m.status='open'
  and f1.next_date<='2012-12-07'
order by f1.next_date desc

Answer 2

尝试这个：

SELECT * FROM main_table AS MT 
LEFT JOIN (SELECT * FROM (SELECT * FROM followups WHERE NDate<='2012-12-07' ORDER BY next_date DESC) AS A GROUP BY eid) AS MF ON MT.eid=MF.eid 
WHERE MT.status='open';

Answer 3

尝试这个

SELECT * FROM main_table AS MT 
LEFT JOIN (SELECT * FROM (SELECT * FROM followups ORDER BY next_date DESC) AS A GROUP BY eid) AS MF ON MT.eid=MF.eid 
WHERE MT.status='open' 
AND MF.NDate<='2012-12-07';