I am trying to perform a clip by attribute in PostGIS between two shapefile containing 3000 polygons. Both shapefiles are free of errors (checked with topology checker), both shapefile are using EPSG:3857.
The following query works well for 99.9% of polygons, but for some it creates incomplete polygons or misses some when loaded in QGIS. The polygons with errors do have the same name used as a clipping attribute. I really don't understand why some polygons fail to be generated compared to others.
create table poly_20m_checked (gid serial PRIMARY KEY, polyID text, geometry geometry); insert into poly_20m_checked(polyID, geometry) select a.name as polyID, ST_Intersection(a.geom,b.geom) as geometry FROM donut20m a, symm20m b WHERE a.name=b.name Group by polyID, geometry
Sample files that contains 4 polygons, among which one that returns an error (moved to make location anonymous): https://drive.google.com/open?id=0B7mqg7Gq1NGVVVVsbTZqMlVhZnc
The reason I am doing it in PostGIS is that I don't think there's a way to clip polygons in 2 shapefiles by using attribute in QGIS. What could be causing errors? I am very open to suggestion to get around the problem. I thought about spliting polygons by ID and then clip each pair of shapefiles but haven't really managed to code it.
EDIT: download for sample polygons. EDIT2: Tried to simplify geometries by 1m, which makes thing a bit better, but still bugy