Add support for aggregate functions (COUNT, SUM, etc)

In fact, the RM model has a notion of ordered objects - every DV_ORDERED for example. But I guess it’s ok not to support that here.

Typo in multiple places: “Integer of Real”; you meant “Integer or Real”.

Funny thing is that most SQL implementations support min and max over strings (maybe just an alias of 'Select stringvalue from table order by stringvalue ASC|DESC limit 1')

In XQuery, min and max functions can be applied over any atomic type, i.e number types dates, times, string and even boolean

I would suggest that if MIN() and MAX() can be used with Strings in real world SQL implementations, then it’s ok for us (although weird for me!); but if not, I wouldn’t do it.

In fact as we use ISO dates order is directly related to string order