Get only country specific result using google geocode api

The correct way of doing this is by providing componentRestrictions

For example:

var request = {
    address: address,
    componentRestrictions: {
        country: 'UK'
    }
}
geocoder.geocode(request, function(results, status){
    //...
});

To restrict results to a specific country use the component-filtering.

The url should be http://maps.googleapis.com/maps/api/geocode/json?address=Singapore%20505468&sensor=false&components=country:SG

But that's not the issue here, the geocoder-result is wrong, because the result has the country set to SG, but the location is wrong(placed in india).

I'm afraid with the given address(it appears that the postcode doesn't exists), the only thing you can do is to report the wrong result to google.

you can set single country or multiple countries

https://maps.googleapis.com/maps/api/place/autocomplete/json?input=Raf&sensor=false&types=(regions)&key=YOUR_API_KEY&components=country:ESP

or

https://maps.googleapis.com/maps/api/place/autocomplete/json?input=Raf&sensor=false&types=(regions)&key=YOUR_API_KEY&components=country:ESP|country:uk|country:us

You should be able to use this approach http://maps.googleapis.com/maps/api/geocode/json?components=country:US|postal_code:5037

remove the address and to the component pass the postal code and make sure if the address has a value let pass another value selected by the user with the postal code to validate your api or else without postal code passed it will leak to another address