So I recently learned about ASSERTION in my databases course, and my prof noted that major databases don't support it, even though it is in the SQL-92 standard. I tried googling to find out why, but there doesn't seem to be any discussion on the topic.
So, why isn't ASSERTION supported by the vast majority of relational database packages? Is it soley a performance issue or is there something intrinsically hard about it?
If you can, please note any database packages that implement it as well (example: if there's an academic/teaching DB). Also, why is there so little discussion on the issue; it's not even mentioned in the Wikipedia page for SQL or SQL-92) But answer the main question first, or answer in comments.
I'm not looking for how to implement it with triggers or anything else.