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Re: sql tables

From: David Cressey <cressey73_at_verizon.net>
Date: Thu, 11 Oct 2007 19:33:00 GMT
Message-ID: <MTuPi.4829$h33.80@trndny02>

"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message news:470e4d35$0$14835$9a566e8b_at_news.aliant.net...
> David Cressey wrote:
>
> > "paul c" <toledobythesea_at_ooyah.ac> wrote in message
> > news:EbrPi.13483$Da.2157_at_pd7urf1no...
> >
> >>(note, I changed the thread subject)
> >>
> >>Bob Badour wrote:
> >>
> >>>David Cressey wrote:
> >>>...
> >>>
> >>>>An SQL DBMS manipulates tables, not relations or relational
variables.
> >>>
> >>>Exactly.
> >>
> >>I presume David could just as well have said "an SQL DBMS manipulates
> >>SQL tables". Found (finally) a copy of some draft or other of the SQL
> >>standard at http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt .
> >>
> >>Not sure how this copy might differ from the official ones, but anyway,
> >>here's some of what it says in section 4.9 which seems to be about
> >>"Concepts":
> >>
> >>
> >>>4.9 Tables
> >>>
> >>> A table is a multiset of rows. A row is a nonempty sequence of
> >>> values. Every row of the same table has the same cardinality
> >
> > and
> >
> >>> contains a value of every column of that table. The i-th value
> >
> > in
> >
> >>> every row of a table is a value of the i-th column of that
> >
> > table.
> >
> >>> The row is the smallest unit of data that can be inserted into
> >
> > a
> >
> >>> table and deleted from a table.
> >>
> >>
> >>I'm wondering if there are popular SQL dbms's that follow this. For
> >>example, do any of them let me "insert", say, two "rows" that would be
> >>considered the same row if a table were a set of rows rather than a
> >>multiset of rows, giving, eg.:
> >>
> >>TableA:
> >>ColumnA
> >>1
> >>1
> >>
> >
> >
> > All of the "major" SQL DBMS products permit storing more than one
identical
> > row in a table. However, they provide several ways the database manager
can
> > protect the database from that event. The simplest is to declare a
primary
> > key for the table. This will also, however, protect against inserting
two
> > rows that differ, but have identical primary key values. Most often,
that
> > coincides with the intent of the manager.
> >
> >
> >>Also wondering about "i-th" values in rows. Does the above also mean
that
> >>
> >>TableB:
> >>ColumnA ColumnB
> >>1 2
> >>
> >>is not equal to
> >>
> >>TableC:
> >>ColumnB ColumnA
> >>2 1
> >>
> >>(all other things being equal)?
> >
> >
> > The question is moot. Table B and Table C have different headers, even
> > though they contain the same columns. a row with values {2, 1}
inserted
> > into TableB would be different from the row that's already there.
> >
> > I'm not nearly as critical of SQL as the relational apologists in this
> > forum. However, I think it's a weakness of SQL that it can't seem to
make
> > up its mind whether to use position or name as way of connecting values
in a
> > list to their "location". I see this confusion all over the language,
and
> > I think it's possible to do better. I am expecting relational
apologists to
> > point out specific languages that actually do better.
>
> No apologies necessary.

Very funny.  "Apologist"  and "apology" have somewhat different meanings,
at least in modern parlance.  Perhaps "apologist" is archaic to begin with.
Perhaps I should have said "proponents"  rather than "apologists".
Received on Thu Oct 11 2007 - 14:33:00 CDT

Original text of this message

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