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I need to append the shapefiles to a PostgreSQL database. Once the data gets appended to PostgreSQL, some topology errors like gaps & overlaps can be seen.
By using the v.clean tools the topology errors can be removed. However, as a result, it gives a separate shapefile ("cleaned").
So how can I remove the topology errors in the given table (test1) in PostgreSQL database?
You can fix the invalid geometries in PostGIS like that:
UPDATE test1 SET geom = ST_MakeValid(geom)
WHERE ST_IsValid(geom) = FALSE;
Note that ST_MakeValid might result in some unwanted lower-dimension geometries ( for example your layer is of type MultiPolygon and you get some resulting Point geometries ), in which case your new geometry column type will GeometryCollection, so you might want to force the return of only one type; maybe MultiPolygon in your case:
update test1 set geom = st_multi(st_collectionextract(st_makevalid(geom),3))
where st_isvalid(geom) = false;
PS: Overlaps and gaps/holes are not invalid geometries, you need to decide yourself what to do with them. You can for instance fill or delete holes between polygons, and for overlaps, you can dissolve them, but this depends entirely on your data and purpose of the analysis.
