XSLT & SQL

Someone told me that he can do *any* XSLT transformation in SQL. Here's the
premise: any input XML document can be represented by one or more tables;
likewise for the output XML document. The XSLT can be replaced with an SQL
insert statement, selecting from the input and inserting to the output
(e.q., any XPath expression can be expressed by a similar WHERE clause in a
SELECT statement).

I can see it's possible for simple document. Are there instances where this
would not be possible?

Thanks.


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