https://gist.github.com/wishdev/635f7a839877d79a6781
Sorry for the 3rd party site - just easier to get the layout correct.....
A CTE and dense_rank is all it takes. I am always amazed at what one can
now pack into such small amounts of code.
On Wed, Jul 23, 2014 at 4:00 PM, Jim Garrison <jim.garri...@nwea.org> wrote:
> I have a collection of relationship rows of the form
>
> Table: graph
> key1 varchar
> key2 varchar
>
> A row of the form ('a','b') indicates that 'a' and 'b' are related.
> The table contains many relationships between keys, forming several
> disjoint sets. All relationships are bi-directional, and both
> directions are present. I.e. the table contains a set of disjoint
> graphs specified as node pairs.
>
> For example the set of values
>
> key1 key2
> ----- -----
> a x
> a y
> b w
> c t
> x a
> y a
> y z
> z y
> t c
> w b
> w d
> d w
>
> defines three disjoint groups of connected keys:
>
> a x y z
> c t
> b w d
>
> What I would like to achieve is a single SQL query that returns
>
> group key
> ----- ---
> 1 a
> 1 x
> 1 y
> 1 z
> 2 c
> 2 t
> 3 b
> 3 w
> 3 d
>
> I don't care about preserving the node-to-node relationships, only
> the group membership for each node.
>
> I've been playing with "WITH RECURSIVE" CTEs but haven't had any
> success. I'm not really sure how to express what I want in SQL, and
> it's not completely clear to me that recursive CTEs will help here.
> Also I'm not sure how to generate the sequence numbers for the groups
>
>
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