Re: Can relational alegbra perform bulk operations?
Date: Wed, 30 Sep 2009 16:34:09 +1000
Message-ID: <EZCwm.251127$vp.33983_at_newsfe12.iad>
Banana wrote:
> exclusively, but my puzzlement definitely dealt with the 'if relational
> theory is supposed to help with this, then why has SQL strayed so far
> from the relational theory as understood in mathematics.')
I believe you've had a good answer in the existence of NULLs and duplicates, but I don't know that SQL is *that* far. The relational algebra doesn't cover the most common four ways to implement an inner join; implementation isn't its concern. But choice of looping, merge joins, hash joins, etc, definitely affects query performance.
>> The change was triggered in part at least by the work of Ken J McDonell >> on the MUSBUS benchmarking tools, who was able to point out the glaring >> differences in actual behaviour of the RDBMS he benchmarked.
> Thank you. I may look his works up and learn a bit about that. It does
> provide a hint (?) toward why the actual implementations is quite
> divorced from the relational theory.
I wish more of his work was still available - I heard him speak about it - but he's still around, see <http://www.kenj.com.au/>. He doesn't live that far from me, and I've thought about looking him up. Perhaps he has some archived material he'd email you?
-- Clifford Heath, Data Constellation, http://dataconstellation.com Agile Information Management and DesignReceived on Wed Sep 30 2009 - 08:34:09 CEST