Add example for rdf_fdw_clone_table() usage

examples/dbpedia-cities-table-cloning.sql

@@ -0,0 +1,40 @@
+CREATE SERVER dbpedia
+FOREIGN DATA WRAPPER rdf_fdw 
+OPTIONS (endpoint 'https://dbpedia.org/sparql');
+
+CREATE FOREIGN TABLE public.cities (
+  uri text       OPTIONS (variable '?city', nodetype 'iri'),
+  city_name text OPTIONS (variable '?name', nodetype 'literal', literaltype 'xsd:string'),
+  area numeric   OPTIONS (variable '?area', nodetype 'literal', literaltype 'xsd:double')
+)
+SERVER dbpedia OPTIONS (
+  log_sparql 'false',
+  sparql '
+    PREFIX dbo:  <http://dbpedia.org/ontology/>
+    PREFIX foaf: <http://xmlns.com/foaf/0.1/>
+    SELECT *
+    {
+      {
+        SELECT ?city ?name ?area
+        {?city a dbo:City ;
+        foaf:name ?name .
+        OPTIONAL {?city dbo:areaTotal ?area}
+      } ORDER BY ASC(?name)
+    }
+  }
+');
+
+/*
+ * materilizes all records from the FOREIGN TABLE 'public.cities' in 
+ * the table 'public.cities_local' - retrieving 5000 records at a time.
+ */ 
+
+CALL rdf_fdw_clone_table(
+      foreign_table => 'cities',
+      target_table  => 'cities_local',
+      create_table => true,
+      fetch_size => 5000,
+      orderby_column => NULL,
+      verbose => true);
+
+SELECT count(*) FROM cities_local;