Re: Can relational alegbra perform bulk operations?
From: Clifford Heath <no.spam_at_please.net>
Date: Wed, 30 Sep 2009 06:48:49 +1000
Message-ID: <Uouwm.147191$nL7.139986_at_newsfe18.iad>
Date: Wed, 30 Sep 2009 06:48:49 +1000
Message-ID: <Uouwm.147191$nL7.139986_at_newsfe18.iad>
Banana wrote:
> Relational algebra, like ordinary algebra, can be employed in help us
> re-formulate the expression into a even simpler expression...
> But... I don't see any means within the relational algebra that provides
> a way of evaluating multiple tuples in one go.
Primitive RDBMS used heuristics to apply transformations to expressions in the hope of reducing execution cost. In the mid 80's, most RDBMS ditched these heuristic optimisers and built cost-based ones. These estimate the execution cost by using statistics (row counts, index selectivity, ordering and clustering of indices, etc), though some, like MySQL, still use heuristics (these are still classed as primitive).
-- Clifford Heath, Data Constellation, http://dataconstellation.com Agile Information Management and DesignReceived on Tue Sep 29 2009 - 22:48:49 CEST