循環遍歷SQL表中的行

Question

我有一個帶有表輸入的存儲過程。我想以某種方式遍歷該表的各行。我不確定你在SQL中如何做這種事情。

這裏就是我試圖做的，在僞SQL：

CREATE PROCEDURE RearrangePuzzles 
    ChangedPuzzles table(
     OldDifficulty nvarchar(50), 
     OldIndex int, 
     NewDifficulty nvarchar(50), 
     NewIndex int 
    ) 
AS 
FOREACH Row IN ChangedPuzzles 
BEGIN 
    UPDATE Puzzles 
    SET Index = Row.NewIndex, 
     Difficulty = Row.NewDifficulty 
    WHERE Index = Row.OldIndex AND 
      Difficulty = Row.OldDifficulty 
END 

這，當然，是不是有效的SQL。我如何在SQL中編寫具有所需功能的查詢？

Answer 1

我認爲在SQL內部採用基於集合的方法通常更好，而不是逐行的解決方案。我相信一個JOIN會在你的情況下工作：

UPDATE p 
SET 
    Index = cp.NewIndex, 
    Difficulty = cp.NewDifficulty 
FROM 
    Puzzles p JOIN 
    ChangedPuzzles cp ON cp.OldIndex = p.Index AND cp.OldDifficulty = p.Difficulty 

Answer 2

你就不能這樣做：

UPDATE Puzzles 
SET 
    Index = cp.NewIndex, 
    Difficulty = cp.NewDifficulty 
FROM ChangedPuzzles cp 
WHERE Index = cp.OldIndex 
AND Difficulty = cp.OldDifficulty 

（這是一個幾個月，因爲我得到了到SQL，所以道歉，如果語法是關閉的）

Answer 3

我可能失去了一些東西，但不這樣完成這個？：

UPDATE Puzzles 
SET  Puzzles.[Index] = ChangesPuzzles.NewIndex, 
     Puzzles.Difficulty = ChangedPuzzles.NewDifficulty 
FROM ChangedPuzzles 
WHERE Puzzles.[Index] = ChangedPuzzles.OldIndex AND Puzzles.Difficulty = ChangesPuzzles.OldDifficulty 

Answer 4

你可以做到這一點通過「更新 - 從」查詢：

UPDATE a 
SET a.Index = b.NewIndex, 
    a.Difficulty = b.NewDifficulty 
FROM Puzzles a 
JOIN ChangedPuzzles b ON a.Index = b.OldIndex AND a.Difficulty = b.OldDifficulty 

Answer 5

你可以使用table-valued parameters（新的SQL Server 2008）：

CREATE TYPE dbo.ChangedPuzzles AS TABLE 
(
     OldDifficulty NVARCHAR(50) NOT NULL, 
     OldIndex INT NOT NULL, 
     NewDifficulty NVARCHAR(50) NOT NULL, 
     NewIndex INT NOT NULL, 
     PRIMARY KEY(OldIndex, OldDifficulty) 
); 
GO 

CREATE PROCEDURE dbo.RearrangePuzzles 
@Source dbo.ChangedPuzzles READONLY 
AS 

UPDATE Puzzles 
SET  Index = src.NewIndex, 
    Difficulty = src.NewDifficulty 
FROM Puzzles p 
INNER JOIN @Source src ON p.Index = src.OldIndex 
AND p.Difficulty = src.OldDifficulty; 
GO 

--Test 
DECLARE @p dbo.ChangedPuzzles; 
INSERT @p VALUES (10,1,11,11), (20,2,22,12); 

EXECUTE dbo.RearrangePuzzles @p;