如何防止触发器触发，以便不将重复数据输入 table

Question

假设我有 3 个这样的 table：

authorGenres (authorGenreId, authorId, isPublished)

bookLibrarys (bookLibraryId, authorGenreId, bookId)

bookList (bookId, authorId)

我创建了一个触发器，当在 authorGenres 中更新行并且 isPublished 列设置为 1.

时触发

发生这种情况时，触发器将一行插入 bookLibrarys table，其中 authorGenreId 列设置为在 authorGenres[= 中更新的行25=]

这是我的工作触发器：

ALTER TRIGGER [dbo].[setCorrectGenreAfterUpdate]
   ON  [dbo].[authorGenres]
   AFTER UPDATE
AS 
BEGIN
    SET NOCOUNT ON;
    DECLARE @bookID AS NVARCHAR(50);
    DECLARE @bookLibraryId AS UNIQUEIDENTIFIER;
    DECLARE @author IDUNIQUEIDENTIFIER;
    SELECT @authorID = Inserted.authorID FROM inserted;

    SET @bookLibraryId = NEWID(); 
    SET @bookID = ( SELECT bookId 
                    FROM booklist nl 
                    WHERE nl.authorID = @authorID)

    INSERT INTO booklibrarys(bookLibraryID, parentBookID, genreID)
    SELECT @bookLibraryId, @bookID, genreID FROM Inserted

END

当我像这样 UPDATE dbo.authorGenres SET isPublished = 1 WHERE genreID = 'C325061D-4274-487B-93F9-03BEB8B7D4D5' 进行测试 UPDATE 时，它会工作并将新行插入 bookLibrarys。

问题是，如果我再次执行该更新，我会在 bookLibrarys 中得到另一个新行，它具有相同的 authorGenreId 和 bookId，但是一个新的 bookLibraryId，因为它是在触发器中生成的。

如果 bookLibrarys 中不存在具有该 bookId 和 authorGenreId 的行，是否有办法仅运行触发？

谢谢！

Answer 1

尝试使用 LEFT JOIN 来检查相同的记录是否已经存在，并确保按照@Lamu 在评论中向您建议的那样具有适用于多行的代码。

像这样：

ALTER TRIGGER [dbo].[setCorrectGenreAfterUpdate]
   ON  [dbo].[authorGenres]
   AFTER UPDATE
AS 
BEGIN
    SET NOCOUNT ON;

    INSERT INTO booklibrarys(bookLibraryID, parentBookID, genreID)
    SELECT NEWID(), bl.bookId, ins.genreID FROM Inserted ins
    INNER JOIN booklist bl ON bl.authorID = ins.authorID -- this is to get  bookId for each row, not for one like in variable
    LEFT JOIN booklibrarys blib ON blib.genreID = ins.genreID AND bl.bookId = 
blib.parentBookID
    WHERE blib.bookLibraryID is NULL
END

如何防止触发器触发，以便不将重复数据输入 table

How to prevent a trigger from firing so that duplicate data is not entered into a table

sql-server

sql-server-2012