separation of church and state?
Date: Sat, 06 Oct 2007 16:06:37 GMT
Message-ID: <hoONi.6504$_K.2827_at_pd7urf3no>
I finally sprung for CJ Date's "Writings, 2000-2006" and skimming it, noticed this point in chapter 10. It reminded me of the recent posts about avoiding books that start with silly sentences even though this quote is from page 174:
"Ordering, by contrast, is not part of the relational algebra; nor can it be, because its result isn't a relation. This doesn't mean you can't have an ORDER BY operator, of course - it just means that operator isn't part of the algebra as such, and it can't be used in an expression that's nested inside some other (relational) expression, or more generally in any context where the result is indeed required to be a relation. That's why you can't use ORDER BY in a view definition, for example."
It seems a little doctrinaire to me. I can agree that the "result isn't a relation" but on the other hand a user could see such a result without knowing that "ORDER BY" was involved and not be faulted for taking it to be a relation. For that matter, in some apps, users take it for granted that all results are arbitrarily ordered and that those results can be used to produce other results.
By analogy of separating the logical from physical implementation, if you want to declare a separation of church and state, I'd think you'd need to mention both. Not to tout SQL but I took the above to mean that if a table were declared with an "INDEX", it shouldn't be allowed to participate in expressions of the relational algebra, which seems extreme and somewhat useless to me.
This is just one small paragraph and I'm not complaining about the rest of the book - Am I mis-interpreting? Received on Sat Oct 06 2007 - 18:06:37 CEST