SQL插入触发器以更新INSERTED表值

Question

我想创建一个Insert触发器,如果​​它们为null,则更新所有插入行的值,根据inserted表中的另一列,新值应从不同的表中获取.

我试过了:

UPDATE INSERTED
SET TheColumnToBeUpdated = 
    (
    SELECT TheValueCol FROM AnotherTable.ValueCol
    WHERE AnotherTable.ValudCol1 = INSERTED.ValueCol1
    )
WHERE ValueCol IS NULL

但我得到这个错误:

Msg 286, Level 16, State 1, Procedure ThisTable_INSERT, Line 15
The logical tables INSERTED and DELETED cannot be updated.

我该怎么办？

Answer 1

您需要更新目标表,而不是逻辑表.但是,您可以使用逻辑表连接以确定要更新的行:

UPDATE YourTable
SET TheColumnToBeUpdated = 
    (
    SELECT TheValueCol FROM AnotherTable.ValueCol
    WHERE AnotherTable.ValudCol1 = INSERTED.ValueCol1
    )
FROM YourTable Y
JOIN Inserted I ON Y.Key = I.Key
WHERE I.ValueCol IS NULL

Answer 2

您可以将触发器更改为INSTEAD OF INSERT.这将允许您检查传入值,如果需要,可以使用其他表中的值替换它们.

CREATE TRIGGER CoolTrigger 
ON MyAwesomeTable 
INSTEAD OF INSERT
AS 
BEGIN  

INSERT MyAwesomeTable (TheValueCol)
SELECT ISNULL(INSERTED.TheValueCol, AnotherTable.TheValueCol) AS TheValueCol
FROM INSERTED
JOIN AnotherTable ON INSERTED.ValueCol1 = AnotherTable.ValueCol1

END

注意:INSTEAD OF触发器不会导致递归.