Re: How does postgres store the join predicate for a relation in a given query

What is meant by "unstructured Join"?

Thanks,
Gourav

On 12 October 2017 at 22:47, Gourav Kumar <gourav1905(at)gmail(dot)com> wrote:

> My objective is to construct join graph from a given query.
> A join graph, has a node for each relation involved in a join, and an edge
> between two relations if they share a join predicate among them.
>
> To do this I first tried to use the make_join_rel() function
> - There I checked if they root->join->cur->level is 2, just write the
> relation names to a file.
> - But this strategy failed, because if there is somewhere a Cartesian
> product among two relations, then they can't have an edge in the join graph.
> - So, along with writing the relation name, I need to know if they
> share a join predicate among them or not.
>
>
> On 12 October 2017 at 22:08, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Gourav Kumar <gourav1905(at)gmail(dot)com> writes:
>> > I have the RelOptInfo data structure for the relations which are to be
>> > joined but when I check their joininfo, it is empty.
>>
>> You aren't telling us anything much about the case you're studying,
>> but if the join clauses have the form of equality comparisons, they
>> likely got converted into EquivalenceClass data structures instead.
>> These days the joininfo lists only contain "unstructured" join
>> conditions.
>>
>> regards, tom lane
>>
>
>
>
> --
> Thanks,
> Gourav Kumar
> Computer Science and Automation
> Indian Institute of Science
>

--
Thanks,
Gourav Kumar
Computer Science and Automation
Indian Institute of Science