As far as I have tested, it looks like the problem could be the cartodb_id. Follow these steps, and you should get the union right:
- First, I recommend applying this query in the dataset view:
SELECT
max(cartodb_id) as cartodb_id,
area_zip_r,
ST_union(the_geom) as the_geom
FROM
zip_rollup_w_modulus_id_copy_1
GROUP BY
area_zip_r
- Secondly, create a new dataset from the query.
- If you count the number of features, the result will be the expected:
2715.