Question

我有一个带表输入的存储过程。我想以某种方式循环遍历该表的行。我不确定你是如何在SQL中做这种事情的。

以下是我在伪SQL中尝试做的事情：

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

当然，这不是有效的SQL。如何在SQL中编写具有所需功能的查询？

Answer 1

我认为通常最好在SQL中采用基于集合的方法，而不是程序化的逐行解决方案。我相信JOIN会适合你的情况：

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

您可以通过“Update-From”查询来执行此操作：

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 3

你不能这样做：

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

（自从我进入SQL以来已经过了几个月，如果语法关闭就道歉了）

Answer 4

我可能会遗漏一些东西，但是这不能实现吗？：

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

Answer 5

您可以使用table-valued parameters（SQL Server 2008中的新增功能）：

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;

循环遍历SQL中的表行

5 个答案: