Re: WWW/Internet 2009: 2nd CFP until 21 September x

Bob Badour wrote:

Walter wants a clue. If every table with null represented a materialized
outer join, as he claims he thinks it does, then presumably something is
being joined. Unnamed perhaps. Implicit for sure. But some ephemeral
tables or relations are joined (outer joined) to materialize the table.

Given a relation with a key K1, ... Kn and remaining attributes
L1, ... Lm, that relation is always the join of the m projections
on K1, ..., Kn, L1, ..., K1, ..., Kn, Lm. What Walter means is
that we can describe 'missing information' NULLs (not all NULLs,
mind you) as the result of allowing such projections to have
fewer rows than the full relation.

This describes tables with NULLs as shorthands
for sets of tables without any NULLs at all,
so it introduces in way that fits perfectly
into the relational model.

If you actually had a clue, rather than just pretending, you wouldn't
call these projections 'unnamed', 'implicit' or 'ephemeral'.

--
Reinier
.

Relevant Pages

  • Re: WWW/Internet 2009: 2nd CFP until 21 September x
    ... outer join, as he claims he thinks it does, then presumably something is ... that relation is always the join of the m projections ... that we can describe 'missing information' NULLs (not all NULLs, ... call these projections 'unnamed', 'implicit' or 'ephemeral'. ...
    (comp.databases.theory)
  • Re: Space required for an empty varchar field?
    ... >who don't understand how to deal with NULLS. ... as they'll be in the result set of an outer join. ... it gets unwieldy fast if you have multiplle NULLable columns. ... Thanks Hugo. ...
    (microsoft.public.sqlserver.programming)
  • Re: Proposal: 6NF
    ... I understand fully the role of the optimizer. ... For example, if you delay arresting a suspected terrorist until you have enough evidence to convict, you get 9/11; if you pick him up and then develop the evidence through interrogation, search and seizure, you may not get enough for a conviction, but you might prevent an attack. ... It's obvious to me that an outer join of a set of restricted projections of a table with nullable columns is equivalent the the original table, provided that each projection does not allow nulls, that each projection includes at least one key and either a subset of the columns that allow nulls or a subset of the columns that don't, and that each column is represented in at least one of the projections. ...
    (comp.databases.theory)
  • Re: WWW/Internet 2009: 2nd CFP until 21 September x
    ... outer join. ... If you can decompose the table into multiple tables each of which has no nulls, what you discover is that a null in the combined table corresponds to an absent row in one of the decomposed tables. ... I'm with you when you suggest that experience counts and I think it's fair ball to point out where an inconsistent theory might produce consistent practical results. ...
    (comp.databases.theory)
  • Re: Second opinion for a query
    ... LEFT OUTER JOIN dbo.tblImage ... You should judge by yourself if you think it's better. ... back to this query in a year or so from now. ... There are a lot of people claiming that NULLs should be avoided, ...
    (microsoft.public.sqlserver.programming)
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