Instead Of Triggers on Views - What's the Use Case?

Our production database is 5-7 years old, and many people have had their hands in it making schema modifications during this time. I just discovered there are Instead Of 开发者_开发问答triggers on some of our views. I didn't even know this was possible. For those of you who have used Instead of triggers on views, what use case were you trying to solve? I'm having a hard time seeing the benefit of this, given the maintainability of doing such a thing.

Thanks very much.

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I haven't used them, but the I think the primary use is allowing INSERT/UPDATE statements to be performed on the view, and having those statements actually INSERT/UPDATE potentially multiple tables underneath the view.

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I have used them to provide a schema which is compatible with a table that an existing application expects to find, but actually perform operations on a completely different schema. This was integrating a bug tracking database system into a database which had an existing user membership system. So the users table that the bug tracking system expected to find was faked up as a view, and INSTEAD OF triggers were implemented to make changes to the membership system that already existed.

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We could probably guess the use case for you if you shared the code. Besides what Chris Shaffer said, these could be to enforce specific data integrity requirements (although truthfully I would expect these on the table not the view) or to add information to fields the user would not normally be aware of.