Sql select table by

Question

我想通過「contactreply」表訂購「contact」表。 「contactreply」表中的「contactid」行是「contact」表中的「ID」行。 「聯繫方式」必須由「contactreply」表中的最後一個插入物訂購，其中「contactid」是表格「contact」中的「ID」。

聯繫表：

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

回覆表

+----+--------+-----------+---------+ 
| 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 | 
+----+--------+-----------+---------+ 

我盡我所能來解釋它，希望你理解它;） 我媒體鏈接看着其他職位，但我不能讓它工作。

預先感謝您。

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

檢查，如果這是你所期望的

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