テーブルをループしてデータセットを見つける方法は?

pivoting で簡単にできます 2 つの方法で行うことができます。

1.Conditional Aggregateを使用する データをピボットします。 pivoting後 datediff を見つけることができます 異なる段階の間。これを試してください。

SELECT orderid,Received,Keyed,Printed,Delivered,
       Datediff(minute, Received, Keyed)    TurnTime1,
       Datediff(minute, Keyed, Printed)     TurnTime2,
       Datediff(minute, Printed, Delivered) TurnTime3
FROM  (SELECT OrderID,
              Max(CASE WHEN ActivityID = 1 THEN ActivityDate END) Received,
              Max(CASE WHEN ActivityID = 2 THEN ActivityDate END) Keyed,
              Max(CASE WHEN ActivityID = 3 THEN ActivityDate END) Printed,
              Max(CASE WHEN ActivityID = 4 THEN ActivityDate END) Delivered
       FROM   Yourtable
       GROUP  BY OrderID)A 

2.pivotingを使用 データを転置する

SELECT orderid,
       [1]                        AS Received,
       [2]                        AS Keyed,
       [3]                        AS Printed,
       [4]                        AS Delivered,
       Datediff(minute, [1], [2]) TurnTime1,
       Datediff(minute, [2], [3]) TurnTime2,
       Datediff(minute, [3], [4]) TurnTime3
FROM   Yourtable
       PIVOT (Max(ActivityDate)
             FOR ActivityID IN([1],[2],[3],[4]))piv