SQL Server ON DELETE Trigger

问题:

I'm trying to create a basic database trigger that conditionally deletes rows from database1.table1 when a row from database2.table2 is deleted. I'm new to triggers and was hoping to learn the best way to accomplish this. This is what I have so far. Suggestions?

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

回答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

回答2:

Better to use:

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

回答3:

INSERTED and DELETED are virtual tables. They need to be used in a FROM clause.

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)

回答4:

I would suggest the use of exists instead of in because in some scenarios that implies null values the behavior is different, so

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