Groups | Search | Server Info | Login | Register

Groups > comp.databases > #99

Re: joining tables and the order changes

Show all headers | View raw

On Jun 25, 2:53 pm, paul c <toledobythe...@yahoo.ca> wrote:
>
> From what I've seen of them, SQL db's are rather comparable in what
> they are able to record.  It is amazing to me that some/most/perhaps
> all SQL dbms'es can't make all the inferences the relational algebra
> requires.  I would have thought that'd be step one in every
> implementation, at least where some effort was made to decide just
> what are the relational requirements.  The bizarre thing is how the
> SQL db's and dbms'es all seem to invent a requirement that is nowhere
> to be found in the algebra or calculus, aka nulls.

Actually, nulls are part of the relational model. Codd added nulls to
RM in 1979 along with 3VL and extensions to relational algebra and
calculus to accommodate the new features (google "Extending the
database relational model to capture more meaning".) He later added
two types of nulls.

No doubt SQL implementations have many quirks and limitations. Even
Standard SQL has its weaknesses, e. g., the EXISTS bug.

Even though Codd himself extended the Relational Model in 1979,
opposition to nulls began to form in the 90's; those opposed include
Date, Darwen, Pascal. 3VL was the original sticking point.

--
Lee Fesperman, FirstSQL Software (http://www.firstsql.com)
=============================================================
* Pure Java implementation, runs on cellphones to mainframes
* FirstSQL/J Object/Relational DBMS (http://www.firstsql.com)

Back to comp.databases | Previous | Next — Previous in thread | Find similar

Thread

joining tables and the order changes shawrie <tourerukcom@googlemail.com> - 2011-06-22 07:44 -0700
  Re: joining tables and the order changes Ben Finney <bignose+hates-spam@benfinney.id.au> - 2011-06-23 07:47 +1000
  Re: joining tables and the order changes Arthur Ward <art.ward@noreply.xx> - 2011-06-23 08:50 +0000
    Re: joining tables and the order changes David Kerber <dkerber@WarrenRogersAssociates.invalid> - 2011-06-23 09:09 -0400
      Re: joining tables and the order changes Arthur Ward <art.ward@noreply.xx> - 2011-06-23 13:23 +0000
        Re: joining tables and the order changes David Kerber <dkerber@WarrenRogersAssociates.invalid> - 2011-06-23 14:35 -0400
    Re: joining tables and the order changes toledobythesea@yahoo.ca - 2011-06-24 10:40 -0700
      Re: joining tables and the order changes Arthur Ward <art.ward@noreply.xx> - 2011-06-25 12:33 +0000
        Re: joining tables and the order changes paul c <toledobythesea@yahoo.ca> - 2011-06-25 14:44 -0700
        Re: joining tables and the order changes paul c <toledobythesea@yahoo.ca> - 2011-06-25 14:53 -0700
          Re: joining tables and the order changes Lee Fesperman <firstsql@gmail.com> - 2011-07-04 00:39 -0700

csiph-web