[postgis-users] SQL syntax question

[Manuel Kohout]

Hi,

I have found following SQL query for measuring distances between polygon
edges:

select a.gid from_gid, b.gid to_gid, st_shortestline(a.geom,b.geom),
st_distance(a.geom,b.geom) as distance
from
test.nfanwood as a,
(select * from test.nfanwood) as b
where st_dwithin(a.geom,b.geom,2000)

https://duncanjg.wordpress.com/2012/09/23/edge-to-edge-distance-using-postgis/

I am a newbie to GIS and wonder, if you could explain the syntax of the
query to me?

It works fine, when I run it with my own polygon shapefile: I receive a
table with 3 columns a-gid, b.gid and distance, containg rows with all
distances of all a.gid to all b.gid.

However, what I'd like is to add the distance from a.gid 1 to b.gid 2,
a.gid 1 to b.gid 3, ... to my existing attribute table where my 103 patches
have ID name "Island" m001 - m103.

Thus all 102 distances of island m001 to all the other 102 islands should
be added as rows with ID name m001.

Is this possible?
/Manu
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