列を更新して同じクエリで元に戻す

Question

SQL Server 2014にテーブルがあり、以前の値に基づいて列を再帰的に更新する必要があります。例えば、

--------------------------------------- 
ID | price | diff_with_prev_price | 
--------------------------------------- 
1 | 29  | 0     | 
2 | 25  | 0     | 
3 | 20  | 0     | 
4 | 35  | 0     | 
5 | 40  | 0     | 
--------------------------------------| 

私は、それは「価格」の次の値を持つ3列目の前の値の合計です

--------------------------------------- 
ID | price | diff_with_prev_price | 
--------------------------------------- 
1 | 29  | 0     | 
2 | 25  | 25     | 
3 | 20  | 5     | 
4 | 35  | -30     | 
5 | 40  | 10     | 
--------------------------------------| 

以下のように再帰的に3番目の列を更新します。 誰かがCTEまたはLEAD/LAGを使用してカーソルを使用せずにこれを行うためのヒントを与えてもらえますか？私は百万行を更新する必要があります。

Answer 1

あなたはこれを試すことができます：あなたが提供

SELECT 1 AS ID , 29 AS price, 0 AS diff_with_prev_prive 
INTO #tmp 
UNION SELECT 2 AS ID , 25 AS price, 0 AS diff_with_prev_prive 
UNION SELECT 3 AS ID , 20 AS price, 0 AS diff_with_prev_prive 
UNION SELECT 4 AS ID , 35 AS price, 0 AS diff_with_prev_prive 
UNION SELECT 5 AS ID , 40 AS price, 0 AS diff_with_prev_prive 

WITH cte AS 
(
    SELECT 
     ID 
     , price 
     , diff_with_prev_prive 
     , price - ISNULL(LAG(price) OVER (ORDER BY ID),0) AS new_value 
    FROM #tmp 
) 
UPDATE t 
SET diff_with_prev_prive = t.new_value 
FROM cte t 

SELECT * FROM #tmp