[英]Joining with the most recently-entered value
I have a table that shows work tickets, basically like this: 我有一张表,显示工作票,基本上是这样的:
TABLE "ticket"
ticket_id INT UNSIGNED AUTO_INCREMENT
created TIMESTAMP DEFAULT CURRENT_TIMESTAMP
ticket_name VARCHAR(64)
Then I have a table showing the possible list of status codes for a ticket: 然后,我有一张表,显示票的可能状态码列表:
TABLE "status_ticket"
status_id INT UNSIGNED AUTO_INCREMENT
created TIMESTAMP DEFAULT CURRENT_TIMESTAMP
status_name VARCHAR(64)
And I have one more table that logs the history of the statuses that a ticket has or has had: 我还有一个表可以记录故障单所具有的状态的历史记录:
TABLE "xref_ticket_status"
xref_id INT UNSIGNED AUTO_INCREMENT
created TIMESTAMP DEFAULT CURRENT_TIMESTAMP
ticket_id INT UNSIGNED NOT NULL
status_id INT UNSIGNED NOT NULL
When the ticket is created, an entry is made in the ticket
table for the ticket, and then an entry is made in the xref_ticket_status
table assigning a status to the ticket by linking the ticket
table to the status_ticket
table. 创建票证后,会在
ticket
表中为该票证创建一个条目,然后在xref_ticket_status
表中创建一个条目,通过将ticket
表链接到status_ticket
表来为票证分配状态。 When the status changes, a new entry is made in the xref_ticket_status
table to reflect the new status. 状态更改时,将在
xref_ticket_status
表中xref_ticket_status
一个新条目以反映新状态。 This way, I have a history of each status that a ticket has had and when it was assigned. 这样,我可以了解故障单所具有的每个状态以及分配时间的历史记录。 The most recent entry for any given
ticket_id
in the xref_ticket_status
table is the ticket's current status. xref_ticket_status
表中任何给定的ticket_id
最新条目是票证的当前状态。
I'm not sure how I would join these three tables together to get a ticket's current status. 我不确定如何将这三个表结合在一起以获取票证的当前状态。 Essentially, I want to join the
ticket
table with the xref_ticket_status
table where ticket_id
matches but for the newest created
column in the xref_ticket_status
. 本质上,我想将
ticket
表与xref_ticket_status
表(其中ticket_id
匹配,但针对ticket_id
中最新created
列)结合xref_ticket_status
。
Thanks! 谢谢!
This should do the trick: 这应该可以解决问题:
select ti.ticket_id,ti.ticket_name,
xr.created, st.status_name
from ticket ti
inner join xref_ticket_status xr
on(ti.ticket_id = xr.ticket_id)
inner join status_ticket st
on(xr.status_id = st.status_id)
group by ti.ticket
order by xr.xref_id desc;
===============Update================== ===============更新==================
select * from
(select ti.ticket_id,ti.ticket_name,
xr.created, st.status_name
from ticket ti
inner join xref_ticket_status xr
on(ti.ticket_id = xr.ticket_id)
inner join status_ticket st
on(xr.status_id = st.status_id)
group by ti.ticket
order by xr.xref_id desc)cs
order by cs.ticket_name desc; //or asc
The following gets the most recent status_id
and ticket_id
from xref_ticket_status
: 下面获取最近
status_id
和ticket_id
从xref_ticket_status
:
select xts.*
from xref_ticket_status xts
where not exists (select 1
from xref_ticket_status xts2
where xts2.ticket_id = xts.ticket_id and
xts2.created > xts.created
);
The logic is: "Get me all rows from xref_ticket_status
where there is no row with the same ticket id and a more recent created date". 逻辑是:“从
xref_ticket_status
获取所有行,其中没有具有相同票证ID和更新日期的行”。 The would be the last date for each ticket. 这将是每张票证的最后日期。 And note that you can also use
xref_id
for the comparison rather than the date. 并请注意,您也可以使用
xref_id
进行比较,而不是使用日期。
The rest is just joining the tables together and choosing your desired columns: 剩下的只是将表连接在一起,然后选择所需的列:
select t.*, ts.*, xts.created
from xref_ticket_status xts join
ticket t
on xts.ticket_id = t.ticket_id join
ticket_status ts
on xts.status_id = ts.status_id
where not exists (select 1
from xref_ticket_status xts2
where xts2.ticket_id = xts.ticket_id and
xts2.created > xts.created
);
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