CREATE SERVER wikidata
FOREIGN DATA WRAPPER rdf_fdw 
OPTIONS (
  endpoint 'https://query.wikidata.org/sparql'
);
CREATE FOREIGN TABLE ft (
  p rdfnode OPTIONS (variable '?p'),
  o rdfnode OPTIONS (variable '?o')
)
SERVER wikidata OPTIONS (
  sparql 'SELECT * {wd:Q192490 ?p ?o}'
);
/* EXPLAIN only */
EXPLAIN
SELECT p, o FROM ft;
                            QUERY PLAN                            
------------------------------------------------------------------
 Foreign Scan on ft  (cost=10000.00..20000.00 rows=1000 width=64)
   Foreign Server: wikidata
   Pushdown: enabled
   Remote Select: ?p ?o 
(4 rows)

EXPLAIN
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100;
                            QUERY PLAN                            
------------------------------------------------------------------
 Foreign Scan on ft  (cost=10000.00..20000.00 rows=1000 width=64)
   Filter: (sparql.isnumeric(o) AND (o > 100))
   Foreign Server: wikidata
   Pushdown: enabled
   Remote Select: ?p ?o 
   Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
(6 rows)

EXPLAIN
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100
ORDER BY o DESC;
                               QUERY PLAN                               
------------------------------------------------------------------------
 Sort  (cost=20049.83..20052.33 rows=1000 width=64)
   Sort Key: o DESC
   ->  Foreign Scan on ft  (cost=10000.00..20000.00 rows=1000 width=64)
         Filter: (sparql.isnumeric(o) AND (o > 100))
         Foreign Server: wikidata
         Pushdown: enabled
         Remote Select: ?p ?o 
         Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
         Remote Sort Key:   DESC (?o)
(9 rows)

EXPLAIN
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100
ORDER BY o DESC
LIMIT 3;
                                  QUERY PLAN                                  
------------------------------------------------------------------------------
 Limit  (cost=20012.92..20012.93 rows=3 width=64)
   ->  Sort  (cost=20012.92..20015.42 rows=1000 width=64)
         Sort Key: o DESC
         ->  Foreign Scan on ft  (cost=10000.00..20000.00 rows=1000 width=64)
               Filter: (sparql.isnumeric(o) AND (o > 100))
               Foreign Server: wikidata
               Pushdown: enabled
               Remote Select: ?p ?o 
               Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
               Remote Sort Key:   DESC (?o)
               Remote Limit: LIMIT 3
(11 rows)

EXPLAIN
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100 OR p IS NOT NULL -- non-pushable condition
ORDER BY o DESC
LIMIT 3;
                                   QUERY PLAN                                   
--------------------------------------------------------------------------------
 Limit  (cost=20012.92..20012.93 rows=3 width=64)
   ->  Sort  (cost=20012.92..20015.42 rows=1000 width=64)
         Sort Key: o DESC
         ->  Foreign Scan on ft  (cost=10000.00..20000.00 rows=1000 width=64)
               Filter: ((sparql.isnumeric(o) AND (o > 100)) OR (p IS NOT NULL))
               Foreign Server: wikidata
               Pushdown: enabled
               Remote Select: ?p ?o 
               Remote Filter: not pushable
               Remote Sort Key:   DESC (?o)
(10 rows)

/* EXPLAIN (VERBOSE) */
EXPLAIN (VERBOSE, COSTS OFF)
SELECT p, o FROM ft;
         QUERY PLAN         
----------------------------
 Foreign Scan on public.ft
   Output: p, o
   Foreign Server: wikidata
   Pushdown: enabled
   Remote Select: ?p ?o 
(5 rows)

EXPLAIN (VERBOSE, COSTS OFF)
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100;
                     QUERY PLAN                      
-----------------------------------------------------
 Foreign Scan on public.ft
   Output: p, o
   Filter: (sparql.isnumeric(ft.o) AND (ft.o > 100))
   Foreign Server: wikidata
   Pushdown: enabled
   Remote Select: ?p ?o 
   Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
(7 rows)

EXPLAIN (VERBOSE, COSTS OFF)
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100
ORDER BY o DESC;
                        QUERY PLAN                         
-----------------------------------------------------------
 Sort
   Output: p, o
   Sort Key: ft.o DESC
   ->  Foreign Scan on public.ft
         Output: p, o
         Filter: (sparql.isnumeric(ft.o) AND (ft.o > 100))
         Foreign Server: wikidata
         Pushdown: enabled
         Remote Select: ?p ?o 
         Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
         Remote Sort Key:   DESC (?o)
(11 rows)

EXPLAIN (VERBOSE, COSTS OFF)
SELECT p, o FROM ft
WHERE sparql.isnumeric(o) AND o > 100
ORDER BY o DESC
LIMIT 3;
                           QUERY PLAN                            
-----------------------------------------------------------------
 Limit
   Output: p, o
   ->  Sort
         Output: p, o
         Sort Key: ft.o DESC
         ->  Foreign Scan on public.ft
               Output: p, o
               Filter: (sparql.isnumeric(ft.o) AND (ft.o > 100))
               Foreign Server: wikidata
               Pushdown: enabled
               Remote Select: ?p ?o 
               Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
               Remote Sort Key:   DESC (?o)
               Remote Limit: LIMIT 3
(14 rows)

EXPLAIN (VERBOSE, COSTS OFF)
SELECT p, o, sparql.sum(o) FROM ft
WHERE sparql.isnumeric(o) AND o > 100 
GROUP BY p, o
ORDER BY o DESC
LIMIT 3;
                              QUERY PLAN                               
-----------------------------------------------------------------------
 Limit
   Output: p, o, (sparql.sum(o))
   ->  GroupAggregate
         Output: p, o, sparql.sum(o)
         Group Key: ft.o, ft.p
         ->  Sort
               Output: p, o
               Sort Key: ft.o DESC, ft.p
               ->  Foreign Scan on public.ft
                     Output: p, o
                     Filter: (sparql.isnumeric(ft.o) AND (ft.o > 100))
                     Foreign Server: wikidata
                     Pushdown: enabled
                     Remote Select: ?p ?o 
                     Remote Filter: ((ISNUMERIC(?o)) && (?o > 100))
                     Remote Sort Key:   DESC (?o)  ASC (?p)
(16 rows)

EXPLAIN (VERBOSE, COSTS OFF)
SELECT p, o, sparql.sum(o) FROM ft
WHERE sparql.isnumeric(o) AND o > 100 OR p IS NOT NULL -- non-pushable condition
GROUP BY p, o
ORDER BY o DESC
LIMIT 3;
                                          QUERY PLAN                                           
-----------------------------------------------------------------------------------------------
 Limit
   Output: p, o, (sparql.sum(o))
   ->  GroupAggregate
         Output: p, o, sparql.sum(o)
         Group Key: ft.o, ft.p
         ->  Sort
               Output: p, o
               Sort Key: ft.o DESC, ft.p
               ->  Foreign Scan on public.ft
                     Output: p, o
                     Filter: ((sparql.isnumeric(ft.o) AND (ft.o > 100)) OR (ft.p IS NOT NULL))
                     Foreign Server: wikidata
                     Pushdown: enabled
                     Remote Select: ?p ?o 
                     Remote Filter: not pushable
                     Remote Sort Key:   DESC (?o)  ASC (?p)
(16 rows)

/* EXPLAIN (VERBOSE) with pushdown disabled */
ALTER FOREIGN TABLE ft OPTIONS (enable_pushdown 'false');
EXPLAIN (VERBOSE, COSTS OFF)
SELECT sparql.str(o), sparql.datatype(o) FROM ft
WHERE sparql.isnumeric(o) AND o > 100
ORDER BY o DESC
LIMIT 3;
                           QUERY PLAN                            
-----------------------------------------------------------------
 Limit
   Output: (sparql.str(o)), (sparql.datatype(o)), o
   ->  Sort
         Output: (sparql.str(o)), (sparql.datatype(o)), o
         Sort Key: ft.o DESC
         ->  Foreign Scan on public.ft
               Output: sparql.str(o), sparql.datatype(o), o
               Filter: (sparql.isnumeric(ft.o) AND (ft.o > 100))
               Foreign Server: wikidata
               Pushdown: disabled
(10 rows)

DROP SERVER wikidata CASCADE;
NOTICE:  drop cascades to foreign table ft