Problems with manipulating Json types

  mongodb, question

There is a Documents in mongodb:

{
 "_id" : ObjectId("54c955492b7c8eb21818bd09"),
 "address" : {
 "street" : "2 Avenue",
 "zipcode" : "10075",
 "building" : "1480",
 "coord" : [ -73.9557413, 40.7720266 ]
 },
 "borough" : "Manhattan",
 "cuisine" : "Italian",
 "grades" : [
 {
 "date" : ISODate("2014-10-01T00:00:00Z"),
 "grade" : "A",
 "score" : 11
 },
 {
 "date" : ISODate("2014-01-16T00:00:00Z"),
 "grade" : "B",
 "score" : 17
 }
 ],
 "name" : "Vella",
 "restaurant_id" : "41704620"
 }

I put it in Greenplum for analysis and stored it in Json type.

create table restaurant(restau json);

Some simple queries can be used;

select restau from restaurant where restau-> restaurant_id='41704620';

But,

select restau from restaurant where restau-> address -> zipcode ='10075';

Why not? Report grammatical errors.

It is suggested to give grammatical errors.