Postgres NoSQL emulation

While reading about NoSQL,

> MongoDB let's you store and search JSON objects.In that case, you don't
> need to have the same "columns" in each "row"

The following ensued. Isn't it cute ?

CREATE TABLE mongo ( id SERIAL PRIMARY KEY, obj hstore NOT NULL );
INSERT INTO mongo (obj) SELECT ('a=>'||n||',key'||(n%10)||'=>'||n)::hstore
 FROM generate_series(1,100000) n;

SELECT * FROM mongo LIMIT 10;
  id |           obj
----+-------------------------
   1 | "a"=>"1", "key1"=>"1"
   2 | "a"=>"2", "key2"=>"2"
   3 | "a"=>"3", "key3"=>"3"
   4 | "a"=>"4", "key4"=>"4"
   5 | "a"=>"5", "key5"=>"5"
   6 | "a"=>"6", "key6"=>"6"
   7 | "a"=>"7", "key7"=>"7"
   8 | "a"=>"8", "key8"=>"8"
   9 | "a"=>"9", "key9"=>"9"
  10 | "a"=>"10", "key0"=>"10"

CREATE INDEX mongo_a ON mongo((obj->'a')) WHERE (obj->'a') IS NOT NULL;
CREATE INDEX mongo_k1 ON mongo((obj->'key1')) WHERE (obj->'key1') IS NOT
NULL;
CREATE INDEX mongo_k2 ON mongo((obj->'key2')) WHERE (obj->'key2') IS NOT
NULL;
VACUUM ANALYZE mongo;

SELECT * FROM mongo WHERE (obj->'key1')='271';
  id  |            obj
-----+---------------------------
  271 | "a"=>"271", "key1"=>"271"
(1 ligne)

EXPLAIN ANALYZE SELECT * FROM mongo WHERE (obj->'key1')='271';
                                                      QUERY PLAN
---------------------------------------------------------------------------------------------------------------------
  Index Scan using mongo_k1 on mongo  (cost=0.00..567.05 rows=513 width=36)
(actual time=0.024..0.025 rows=1 loops=1)
    Index Cond: ((obj -> 'key1'::text) = '271'::text)
  Total runtime: 0.048 ms