Sql select table by

Question

我想通过“contactreply”表订购“contact”表。 “contactreply”表中的“contactid”行是“contact”表中的“ID”行。 “联系方式”必须由“contactreply”表中的最后一个插入物订购，其中“contactid”是表格“contact”中的“ID”。

联系表：

+----+--------+----------+----------+ 
| ID | userid | subject | content | 
+----+--------+----------+----------+ 
| 1 |  1 | subject | subject | 
| 2 |  1 | subject2 | subject2 | 
+----+--------+----------+----------+ 

回复表

+----+--------+-----------+---------+ 
| ID | userid | contactid | content | 
+----+--------+-----------+---------+ 
| 1 |  1 |   1 | reply1 | 
| 2 |  1 |   2 | reply2 | 
| 3 |  1 |   1 | fasd | 
| 4 |  1 |   2 | asdf | 
| 5 |  1 |   2 | f  | 
| 6 |  1 |   1 | asdf | 
+----+--------+-----------+---------+ 

我尽我所能来解释它，希望你理解它;） 我媒体链接看着其他职位，但我不能让它工作。

预先感谢您。

Answer 1

SELECT c.* 
    FROM contacts c 
    JOIN reply x 
    ON x.contactid = c.id 
    JOIN 
    (SELECT MAX(id) max_id FROM reply GROUP BY contactid) y 
    ON y.max_id = x.id 
ORDER 
    BY x.id; 
+----+--------+----------+----------+ 
| ID | userid | subject | content | 
+----+--------+----------+----------+ 
| 2 |  1 | subject2 | subject2 | 
| 1 |  1 | subject | subject | 
+----+--------+----------+----------+ 

Answer 2

检查，如果这是你所期望的

select a.*, b.id from contact as a 
     inner join 
(select * from contactReply as x 
where x.id = 
      (select max(id) from contactReply as y 
      where x.contactid = y.contactid) 
) as b 
on a.ID = b.contactId 
order by b.id