I have looked over this addition, and I think I finally understand it.
Given three tables, A, B, C, which join as A->B, B->C, C->A, you can
really join them as A->B->C, and A->C->B. What full disjunction does is
to perform both of those joins, and return a one row for each join. Here
is an example from the README:
Example of an input and output of a full disjunctions: INPUT:
--A---|---B---|---C-- X---Y-|-Y---Z-|-X---Z a-|-b-|-b-|-c-|-a-|-d
A,B and C are relations. X,Y and Z are attributes. a,b,c and d are values.
Note that A,B and C are connected in a cycle. That is: A is connected to B on attribute Y, B is connected to C
onattribute Z, C is connected to A on attribute X.
The output of the full disjunctions FD(A,B,C):
FD X---Y---Z a-|-b-|-c a-|-b-|-d
This code is pretty complex, so I can see why it should be in /contrib.
Are there reasonable use cases for this capability?
---------------------------------------------------------------------------
Tzahi Fadida wrote:
> Hi,
> I wish to add the fulldisjunctions function to the contrib.
> With the help of Jonah, we (or rather he :) created a patch with
> regression tests. The function is finished programmatically but
> still a little more code documentation touches and improved error messages
> are needed. All the rest was extensively tested.
>
> Attached is the patch.
>
> Works great. Just compiled from a fresh cvs which i patched with the
> attached diff. ran the fulldijsjunction.sql in the
> share/contrib/fulldisjunction and let it run and it works great.
> 10x.
>
> --
> Regards,
> ????????Tzahi.
> --
> Tzahi Fadida
> Blog: http://tzahi.blogsite.org | Home Site: http://tzahi.webhop.info
> WARNING TO SPAMMERS: ?see at
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