[GRLUG] Database query logic

[megadave]

the filter is the "where" clause.

select name, phone, email from people where email like '%yahoo.com'.

the filter is the part where it only shows records that match "yahoo.com".


On Fri, Feb 3, 2012 at 17:44, Eric Beversluis
<ebever at researchintegration.org> wrote:
> I've been doing some reading on The Raiser's Edge. I found it
> interesting  that, when explaining queries, they emphasized that the
> queries do "filtering." This raised the question for me whether
> relational DB queries actually "filter" or whether the RE talk of
> "filtering" is heuristic.
>
> In other words, which of these two descriptions fits how a database
> query works?
> 1. The "selection" method: If I say "select FName from tblPeople," the
> programs opens a file and "copies" all the FName values to a new file
> (or into memory).
> 2.  The "filter" method: If I say "select FName from tblPeople," the
> program opens a file, deletes everything that is not "FName," and saves
> the result to a new file (or into memory).
>
> It seems to me that these two approaches are in fact different and would
> be programmed very differently.
>
> I've never thought of DBs as using the "filter" approach, but then I
> haven't thought very hard about it either.
>
> Are these in fact two different logical approaches? If so, which do
> relational DBs use--or do some use one approach and some the other?
>
>
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