[英]How to SELECT data from two tables which only first row of second table is selected for one row of first table
[英]select from two tables ordering by one row from second table
我有两个表, tickets
和ticket_updates
有在多行ticket_updates
在每一个行tickets
如何在ticket_updates
按datetime
时间从订购tickets
中ticket_updates
我想从最早的datetime
(DESC)在ticket_updates
按datetime
时间进行订购
我以为以下方法可能有效,但是在PHPMyAdmin中运行需要太长时间,并且出现内部服务器错误:
SELECT t.ticketnumber, t.subject, t.contact_name FROM tickets t JOIN ticket_updates tu on t.ticketnumber = tu.ticketnumber group by tu.ticketnumber order by tu.datetime DESC
您可以执行以下操作:
select t.*
from tickets t
order by (select min(datetime) from ticket_updates tu where tu.ticketid = t.ticketid);
编辑:
您也可以尝试以下group by
:
select t.*
from tickets t join
(select ticketid, min(datetime) as mindt
from ticket_updates tu
group by ticketid
) tu
on tu.ticketid = t.ticketid
group by tu.mindt desc;
或者,原始查询可以利用ticket_updates(ticketid, datetime)
上的索引。
我认为您想要这样的东西,这几乎是您编辑后发布的内容。 如果运行太慢,则可能需要对查询运行EXPLAIN并添加适当的索引。 就像戈登建议的那样,要么是日期时间,要么是票号/日期时间的复合键。
SELECT t.ticketnumber, t.subject, t.contact_name FROM ticket_updates tu
INNER JOIN tickets t ON t.ticketnumber = tu.ticketnumber
GROUP BY tu.ticketnumber
ORDER BY tu.datetime DESC
要么
SELECT t.ticketnumber, t.subject, t.contact_name FROM ticket_updates tu
INNER JOIN tickets t using(ticketnumber)
GROUP BY tu.ticketnumber
ORDER BY tu.datetime DESC
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