数据库中有表countries。在pgAdmin中查看如下：

在QGIS中查看如下：

1.将国家按照区域划分，并合并几何。

SELECT 
MIN(subregion) AS subregion,
SUM(pop2005) AS pop2005From,
ST_union(the_geom) AS the_geom 
FROM public.countries 
GROUP BY subregion;

在pgAdmin中查看如下：

 2.将查询结果输出到shapefile

pgsql2shp -f subregions.shp -h localhost -u postgres -P postgres postgis_32_sample "SELECT MIN(subregion) AS subregion,SUM(pop2005) AS pop2005 From,ST_union(the_geom) AS the_geom FROM public.countries GROUP BY subregion; "

在QGIS中查看shapefile如下：