[GIS] ST_Touches for more than just one geometry

postgispostgis-2.0postgresql

I'd like to select some neighbor polygons with ST_Touches. Therefore I found the following statement:

SELECT b.name
FROM layera as a
JOIN layera as b
  ON ST_Touches((SELECT a.geom FROM layera as a WHERE a.id = 5124),b.geom)
GROUP BY b.name

With this I get all the neighbor polygons of the polygon with the id '5124'. But now I want to call this function with a list of arguments. See the example statment below:

SELECT b.name
FROM layera as a
JOIN layera as b
  ON ST_Touches((SELECT a.geom FROM layera as a WHERE a.id > 5000),b.geom)
GROUP BY b.name

(SELECT a.geom FROM layera as a WHERE a.id > 5000 returns lets say 100 results)

I know that this won't work because ST_Touches works for only two arguments. But this should show what I'd like to do. How is it possible to insert all the results of a SELECT-statement into this ST_Touches function?

Thanks for any suggestions. =)

EDIT:

Ok, I just found out that I get the same result set with this statement:

SELECT layera.name
FROM layera
WHERE ST_Touches(layera.geom,(SELECT layera.geom FROM layera WHERE layera.nr = 5134))

Anyway, the problem isn't solved. =(

Best Answer

If I understand you right, you have just complicated the syntax a little:

SELECT a.nr, b.nr FROM
layera AS a INNER JOIN layera AS b 
ON ST_Touches(a.geom, b.geom) 
WHEREa.nr!=b.nr AND b.nr < 5000;

Then you will get a list of all combinations between the first 4999 numbers and the rest.

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