Mikito Harakiri wrote:
> Mikito Harakiri wrote:
>
>>Transitive closure (TC) of a graph is
>>
>>with TransClosedEdges (tail, head) as
>>( select tail, head from Edges
>> union all
>> select e.tail, ee.head from Edges e, TransClosedEdges ee
>> where e.head = ee.tail
>>)
>>select distinct * from TransClosedEdges
>>
>>except that this query might never terminate.
>
>
> Oops, it's actually quite obvious
>
> with TransClosedEdges (tail, head) as
> ( select tail, head from Edges
> where tail <> head --*******
> union all
> select e.tail, ee.head from Edges e, TransClosedEdges ee
> where e.head = ee.tail
> and e.tail <> ee.head --*******
> )
> select distinct * from TransClosedEdges
>
> Graeme handles more general case, hence the complication.
>
There will be a new developerWorks article on mapping CONnECT BY to DB2
tomorrow (if all goes well).
Cheers
Serge
--
Serge Rielau
DB2 SQL Compiler Development
IBM Toronto Lab
Received on Wed Oct 12 2005 - 06:23:13 CDT
