获取记录的历史记录

Question

我的表格包含两列RequestId和OldRequestId。

• 如果我传递RequestId，它应该会检索我的具体记录。

• 如果检索到的记录中的OldRequestId不为空，那么它也应该带来旧的请求数据。

• 它应该继续，直到OldRequestId为空。

有人可以帮助我为此要求编写最好的SQL查询吗？

Answer 1

您可以使用递归公用表表达式（CTE）解决此问题：

DECLARE
   @RequestID int = 6;

WITH
   ReqCTE AS
      (
         SELECT
               RequestID,
               OldRequestID
            FROM
               Requests
            WHERE
               RequestID = @RequestID
         UNION ALL SELECT
               R.RequestID,
               R.OldRequestID
            FROM
               ReqCTE C
               INNER JOIN Requests R
                  ON R.RequestID = C.OldRequestID
      )
SELECT
      *
   FROM
      ReqCTE;

Answer 2

答案取决于您希望将旧请求链接到替换项的深度。如果它只是一个级别，您可以制作一个简单的LEFT JOIN：

SELECT  
  n.RequestID,
  COALESCE(r.RequestID, n.RequestID) AS CurrentRequestID,
  n.OldRequestID
FROM
  Requests n LEFT JOIN 
  Requests r ON n.RequestID = r.OldRequestID
WHERE 6 IN (r.RequestID, n.RequestID) 

由于您希望将旧请求链接到最新请求，因此您需要使用CTE递归执行此操作：

WITH CurrentRequests AS (
  SELECT
    id,
    RequestID,
    OldRequestID ,
    RequestID as TopRequestID
  FROM
    Requests
  UNION ALL SELECT
    R.id,
    R.RequestID,
    R.OldRequestID, 
    C.TopRequestID as TopRequestID
  FROM
    CurrentRequests C
    INNER JOIN Requests R
      ON R.RequestID = C.OldRequestID
)
SELECT *
FROM
 CurrentRequests 
WHERE TopRequestID  = 6;