带有内连接、子选择和限制的 SQL 选择

Question

我已经处理这个 SQL 问题大约 2 天了，我怀疑我非常接近解决这个问题，但似乎无法找到完全有效的解决方案。

我正在尝试对两个名为 application_info 和 application_status 的表进行选择性连接，这些表用于存储有关开放获取期刊文章资助请求的信息。

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、已资助、已拒绝、已撤回等）以及期刊文章状态（已提交、已接受、重新提交、已发表或已拒绝）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。

因为我们想要保留应用程序、文章和资金状态更改的运行日志，我们不想用更新的值覆盖application_status 中的现有行，而是只想显示最新的状态值。因为应用程序最终将有多个状态更改，所以需要对应用程序数据的状态数据的内部连接应用某种限制，以便每个应用程序 ID 只返回一行。

这是我在当前引发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 和部分子查询以及LIMIT 会导致选择工作，但会为给定应用程序ID 的每个状态返回一行。我尝试过使用MIN/MAX 运算符，但注意到它们在工作时会从application_status 表中返回不可预测的行。

我也尝试在连接的ON 部分中进行子选择，但不知道如何实现，因为最终结果总是需要返回Application_ID（两者都可以@987654338 @ 和 Status_ID 被退回并使用？）。

关于如何让它按我的意图工作的任何提示？这也能做到吗？

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，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 子句中不能有相关子查询。

试试这个想法：

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
. . .

即把关联的子查询放在select子句中，获取最新的状态。然后将其加入状态表以获取其他信息。并且，使用其他详细信息完成查询。

您似乎很擅长您的 SQL 技能，因此似乎没有必要为您重写整个查询。