Question

我正在尝试创建一个基本数据库触发器，当删除database2.table2中的一行时，它会有条件地从database1.table1中删除行。我是触发器的新手，并希望学习实现这一目标的最佳方法。这就是我到目前为止所拥有的。建议？

CREATE TRIGGER sampleTrigger
    ON database1.dbo.table1
    FOR DELETE
AS
    IF EXISTS (SELECT foo
               FROM database2.dbo.table2
               WHERE id = deleted.id
               AND bar = 4)

-- If there is a row that exists in database2.dbo.table2 
-- matching the id of the deleted row and bar=4, delete 
-- it as well.

-- DELETE STATEMENT?

GO

Answer 1

CREATE TRIGGER sampleTrigger
    ON database1.dbo.table1
    FOR DELETE
AS
    DELETE FROM database2.dbo.table2
    WHERE bar = 4 AND ID IN(SELECT deleted.id FROM deleted)
GO

Answer 2

最好使用：

DELETE tbl FROM tbl INNER JOIN deleted ON tbl.key=deleted.key

Answer 3

INSERTED和DELETED是虚拟表。它们需要在FROM子句中使用。

CREATE TRIGGER sampleTrigger
    ON database1.dbo.table1
    FOR DELETE
AS
    IF EXISTS (SELECT foo
               FROM database2.dbo.table2
               WHERE id IN (SELECT deleted.id FROM deleted)
               AND bar = 4)

Answer 4

我建议使用exists代替in，因为在某些情况下暗示空值the behavior is different，所以

CREATE TRIGGER sampleTrigger
    ON database1.dbo.table1
    FOR DELETE
AS
    DELETE FROM database2.dbo.table2 childTable
    WHERE bar = 4 AND exists (SELECT id FROM deleted where deleted.id = childTable.id)
GO

SQL Server ON DELETE触发器

4 个答案: