SQL选择与内部联接，子选择和限制

Question

我一直在使用这个SQL问题约2天，现在怀疑我非常接近解决问题，但似乎无法找到一个解决方案，完全作品。

我试图做的是在两个表上选择性连接，称为application_info和application_status，用于存储有关开放获取期刊文章资助请求的信息。

application_info具有关于申请人的一般信息，并使用称为Application_ID的自动索引字段作为关键字段。 application_status用于追踪有关申请状态（已收到，正在审阅，资助，拒绝，撤回等）以及期刊文章状态（提交，接受，重新提交，发布或拒绝）的持续信息，并包含Application_ID字段和名为Status_ID的自动索引字段以及状态文本和状态日期字段。

由于我们希望保持应用程序，文章和资金状态更改的运行日志，因此我们不希望用更新的值覆盖application_status中的现有行，而只想显示最新的状态值。由于应用程序最终会有多个状态更改，因此需要对应用程序数据的状态数据的内部联接应用某种限制，以便每个应用程序标识只返回一行。

这里就是我试图在当前引发错误的查询做的一个例子：

-- simplified example 
SELECT 
application_info.*, 
artstatus.Status_ID AS Article_Status_ID, 
artstatus.Application_ID AS Article_Application_ID, 
artstatus.Status_State_Date AS Article_Status_State_Date, 
artstatus.Status_State_Text AS Article_Status_State_Text 
FROM application_info 
LEFT JOIN (
    SELECT 
    Status_ID, 
    Application_ID, 
    Status_State_Text, 
    Status_State_Date, 
    Status_State_InitiatedBy, 
    Status_State_ChangebBy, 
    Status_State_Notes 
    FROM application_status 
    WHERE Status_State_Text LIKE 'Article Status%' 
    AND Application_ID = application_info.Application_ID -- how to pass the current application_info.Application_ID from the ON clause to here? 
    -- and Application_ID = 29 -- this would be an option for specific IDs, but not an option for getting a complete list of application IDs with status 
    -- GROUP BY Application_ID -- reduces the sub query to 1 row (Yeah!) but returns the first row encountered before the ORDER BY comes into play 
    ORDER BY Status_ID DESC 
    -- a GROUP BY after the ORDER BY might resolve the issue if we could do a sort first 
    LIMIT 1 -- only want to get the first (most recent) row, only works correctly if passing an Application_ID 
) AS artstatus 
ON application_info.Application_ID = artstatus.Application_ID 
-- WHERE application_info.Application_ID = 29 -- need to get all IDs with statu values as well as for specific ID requests 
; 

省去了AND Application_ID = application_info.Application_ID而且随着LIMIT导致选择工作的子查询的一部分，但为给定应用程序ID的每个状态返回一行。我尝试过使用MIN/MAX运营商，但注意到它们在工作时会从application_status表中返回不可预测的行。

我也试图做子在选择的加盟ON部分，但不知道如何使这项工作，因为最终的结果总是需要返回Application_ID（既可以Application_ID和Status_ID返回并用？）。

任何提示如何让这个工作，因为我打算？这甚至可以完成？

进一步编辑：下面的工作查询。关键是将联合中的子查询更深入地移动一层，然后只返回一个状态ID。

-- simplified example (now working) 
SELECT 
application_info.*, 
artstatus.Status_ID AS Article_Status_ID, 
artstatus.Application_ID AS Article_Application_ID, 
artstatus.Status_State_Date AS Article_Status_State_Date, 
artstatus.Status_State_Text AS Article_Status_State_Text 
FROM application_info 
LEFT JOIN (
    SELECT 
    Status_ID, 
    Application_ID, 
    Status_State_Text, 
    Status_State_Date, 
    Status_State_InitiatedBy, 
    Status_State_ChangebBy, 
    Status_State_Notes 
    FROM application_status AS artstatus_int 
    WHERE 
    -- sub query moved one level deeper so current join Application_ID can be passed 
    -- order by and limit can now be used 
    Status_ID = (
     SELECT status_ID FROM application_status WHERE Application_ID = artstatus_int.Application_ID 
     AND status_State_Text LIKE 'Article Status%' 
     ORDER BY Status_ID DESC 
     LIMIT 1 
    ) 
    ORDER BY Application_ID, Status_ID DESC 
    -- no need for GROUP BY or LIMIT here because only one row is returned per Application_ID 
) AS artstatus 
ON application_info.Application_ID = artstatus.Application_ID 
-- WHERE application_info.Application_ID = 29 -- works for specific application ID as well 

-- more LEFT JOINS follow 
; 

Answer 1

在from子句中不能有相关的子查询。

试试这个想法来代替：

select <whatever> 
from (select a.*, 
      (select max(status_id) as maxstatusid 
       from application_status aps 
       where aps.application_id = a.application_id 
      ) as maxstatusid 
     from application 
    ) left outer join 
    application_status aps 
    on aps.status_id = a.maxstatusid 
. . . 

也就是说，把相关子查询的SELECT子句中，以获得最新的状态。然后将其加入状态表以获取其他信息。并且，用其他细节完成查询。

你似乎很擅长你的SQL技能，所以似乎没有必要为你重写整个查询。