[Q] SQL3 trigger modes(before,after,insteadof) difference?

[ please CC: to me when you reply ]

I'm trying to understand the real difference of three trigger modes in SQL3 -- immediate before/after/insteadof. It is my understanding that when the rules are considered or when the action is executed, etc. among three modes are all different as shown below.

    before         : C->A->E
    after            : E->C->A
    insteadof     : C---->A

However, i'm not sure when one is absolutely necessary over the other; that is, is there any case when immediate-before trigger can do, but not ther other modes? Or when immediate-insteadof mode can, but immediate-after cannot, etc.? Given certain constraint to enforce or some application logic, if performance is not concern, is that true that any of three trigger modes will eventually lead to identical database states?

My guess is that there must be some compelling reasons; 'cause otherwise ISO-ANSI wouldn't make it that way..

sincerely.

--
Don Received on Sun May 16 1999 - 23:16:48 CDT