Обсуждение: doc fix

I think this is right..

Patrick

Index: sql.sgml
===================================================================
RCS file: /projects/cvsroot/pgsql/doc/src/sgml/sql.sgml,v
retrieving revision 1.24
diff -p -r1.24 sql.sgml
*** sql.sgml    2001/10/23 16:42:36    1.24
--- sql.sgml    2002/02/11 15:37:47
*************** attributes are taken from. We often writ
*** 488,494 ****

        <listitem>
         <para>
!     DIFFERENCE (− or ∖): builds the set difference of
      two tables. Let <classname>R</classname> and <classname>S</classname>
      again be two tables with the same
      arity. <classname>R</classname> - <classname>S</classname>
--- 488,494 ----

        <listitem>
         <para>
!     EXCEPT (− or ∖): builds the set difference of
      two tables. Let <classname>R</classname> and <classname>S</classname>
      again be two tables with the same
      arity. <classname>R</classname> - <classname>S</classname>

Patrick Welche writes:

> I think this is right..

No, it's talking about relational algebra, not SQL.

>
> Patrick
>
> Index: sql.sgml
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/doc/src/sgml/sql.sgml,v
> retrieving revision 1.24
> diff -p -r1.24 sql.sgml
> *** sql.sgml    2001/10/23 16:42:36    1.24
> --- sql.sgml    2002/02/11 15:37:47
> *************** attributes are taken from. We often writ
> *** 488,494 ****
>
>         <listitem>
>          <para>
> !     DIFFERENCE (− or ∖): builds the set difference of
>       two tables. Let <classname>R</classname> and <classname>S</classname>
>       again be two tables with the same
>       arity. <classname>R</classname> - <classname>S</classname>
> --- 488,494 ----
>
>         <listitem>
>          <para>
> !     EXCEPT (− or ∖): builds the set difference of
>       two tables. Let <classname>R</classname> and <classname>S</classname>
>       again be two tables with the same
>       arity. <classname>R</classname> - <classname>S</classname>
>

--
Peter Eisentraut   peter_e@gmx.net

Patrick Welche <prlw1@newn.cam.ac.uk> writes:
> I think this is right..

I think not.  The section in question is defining the mathematical
terms of set theory, not their representation in SQL.

(BTW, is this file even still used?  Right offhand I can't see it
anywhere in the 7.2 documentation set.)

            regards, tom lane

On Mon, Feb 11, 2002 at 11:43:45AM -0500, Tom Lane wrote:
> Patrick Welche <prlw1@newn.cam.ac.uk> writes:
> > I think this is right..
>
> I think not.  The section in question is defining the mathematical
> terms of set theory, not their representation in SQL.
>
> (BTW, is this file even still used?  Right offhand I can't see it
> anywhere in the 7.2 documentation set.)

I have no idea, I just grep -i intersect * in doc/src/sgml and sql.sgml
seemed to have the right sort of list in it, just that whereas UNION
and INTERSECT have direct correspondence to SQL, DIFFERENCE <-> EXCEPT,
so it just looked wrong to me. So, please ignore..

Cheers,

Patrick

On Mon, Feb 11, 2002 at 11:07:19AM -0500, Peter Eisentraut wrote:
> Patrick Welche writes:
>
> > I think this is right..
>
> No, it's talking about relational algebra, not SQL.

OK please ignore it then.. I was trying to do (A union B) - (A intersection B)
and wondered what to use as the -. Read sql.sgml to find union, intersect,
and found no DIFFERENCE in gram.y, so thought that the list was wrong.

Cheers,

Patrick