Counting distinct undirected edges in a directed graph in SQL?

Select count(*) from ( select to_there from edges where from_here = 1 union select from_here from edges where to_there = 1 ) as whatever.

Right, "The result of UNION does not contain any duplicate rows unless the ALL option is specified. " (postgresql. Org/docs/current/static/sql-select.

Html#SQL-UNION). That'll teach me not to RTFM. – mu is too short Mar 10 at 20:32 PostgreSQL (at least my version) wants an alias for the "(... union ...)" but I'll add that and go with this one as this UNION is simpler than Thomas's EXCEPT.

– mu is too short Mar 10 at 20:44.

If it were the case that for every edge, there was a reciprocal (e.g. If (1,2) exists, then (2,1) must exist), then you could simply narrow your list like so: Select Count(*) From edges Where from_here.

1 Well done sir. – Dane Mar 10 at 20:36 +10 for teaching me something new (i.e. EXCEPT) but I'm going to go with the UNION as it is a bit simpler.

– mu is too short Mar 10 at 20:41.

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