Question

我一直在处理这个SQL问题大约2天，并怀疑我非常接近解决问题，但似乎无法找到完全有效的解决方案。

我正在尝试做的是选择性加入两个名为application_info和application_status的表，这两个表用于存储有关开放访问期刊文章资金请求的信息。

application_info包含有关申请人的一般信息，并使用名为Application_ID的自动索引字段作为关键字段。 application_status用于跟踪有关申请状态（已收到，正在审核，资助，拒绝，撤回等）以及期刊文章状态（提交，接受，重新提交，已发布或已发布）的持续信息。拒绝）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。

由于我们希望保留应用程序，文章和资金状态更改的运行日志，因此我们不希望使用更新的值覆盖application_status中的现有行，而是希望仅显示最新状态值。由于应用程序最终会有多个状态更改，因此需要对状态数据的内部联接应用某种限制，以便为每个应用程序ID返回一行。

以下是我在当前抛出错误的查询中尝试执行的操作的示例：

-- 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
;

消除AND Application_ID = application_info.Application_ID和子查询的一部分以及LIMIT会导致select工作，但会为给定的应用程序ID的每个状态返回一行。我已经尝试过使用MIN / MAX运算符，但是注意到它们工作时会从application_status表返回不可预测的行。

我还尝试在联接的ON部分中进行子选择，但不知道如何使其工作，因为最终结果始终需要返回Application_ID（是否可以返回并使用Application_ID和Status_ID？）。

有关如何让我按照我的意图工作的任何提示？甚至可以这样做吗？

进一步编辑：下面的工作查询。关键是将连接中的子查询更深一层地移动，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。

请尝试这个想法：

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，将相关子查询放在select子句中以获取最新状态。然后将其加入状态表以获取其他信息。并使用其他详细信息完成查询。

您似乎非常擅长自己的SQL技能，所以似乎没有必要为您重写整个查询。

SQL选择内连接，子选择和限制

1 个答案: