[GIS] How to find polygons inside polygon with PostGIS 2.0

postgispostgis-2.0

I have a relation representing all the counties in my country and the other one containing all the districts – e. g. each and every county is composed of several districts.
How do I select them with spatial query?
I tried with 

select nazorp from kraje as k, orp_wgs as o WHERE ST_Within(o.geom,k.geom) AND
k.nazev = 'Liberecký'

but had wrong results returned (well, they are probably not wrong, they are just not what I expected them to be). ST_Within only returns districts that don't share a boundary with the county, but I need to get all the districts within the county. Is that possible?
I haven't found any built-in function suitable for my needs yet.

Best Answer

Use ST_Contains, which will not reject the border if you are working with polygons (a linestring on the boundary of the original would fail, but that's a special case).

edit:

select nazorp from kraje as k, orp_wgs as o WHERE ST_Intersects(o.geom,k.geom) 
AND k.nazev = 'Liberecký'
AND ST_Area(ST_Intersection(o.geom,k.geom)) != ST_Area(o.geom)

This was just a check that the data is sane. Nothing should be returned, but if it is, treat those districts with care. To get what you initially wanted, just omit the last condition (faster) or change the comparison to an equality check.

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