postgis query for addresses (with osm data)

I want to make queries for addresses to postgis database with data from openstreetmap, check if such address exist in database and if so, get coordinates. Database was filled from .pbf file using osmosis. This is schema for the database http://pastebin.com/Yigjt77f. I have addresses in form of city name, street name and number of street. The most important for me is this table:

CREATE TABLE node_tags (
    node_id BIGINT NOT NULL,
    k text NOT NULL,
    v text NOT NULL
);

k column is in form of tags, one that I'm interested are: addr:housenumber, addr:street, addr:city and v is corresponding value. First I'm searching if name of city matches one in database, than in results set I'm searching for street and than for house number. The problem is that I don't know how to make SQL query that will get this result with asking only once. I can ask first only for city name, get all node_id that match my city and save them in java program, than make queries asking for each found(matching my city) id_number (list from my java program) for the street, and so on. This way is really slow, because asking for more detailed information (city than street than number) I have to make more and more queries and what is more I have to check a lot of addresses. Once I have matching node_id I can easily find coordinates, so that's not a problem.

Example of this table:

    node_id | k | v <br>
    123 | addr:housenumber | 50
    123 | addr:street | Kingsway
    123 | addr:city | London
    123 | (some other stuff) | .....
    100 | addr:housenumber | 121
    100 | addr:street | Edmund St
    100 | addr:city | London

I hope I explained clearly what is my problem.

This is not as easy as you might think. Addresses in OSM are hierarchically, like in the real world. Not all elements in OSM have a full address attached. Some only have addr:housenumber and simply belong to the nearest street. Some have addr:housenumber and addr:street but no addr:city because they simply belong to the nearest city. Or they are enclosed by a boundary relation which specifies the corresponding city. And instead of addr:housenumber there are sometimes also just address interpolations described by the addr:interpolation key. See the addr key wiki page for more information.

The Karlsruhe Schema page in the OSM wiki explains a lot about addresses in OSM. It also mentions associatedStreet relations which are sometimes used to group house numbers and their corresponding streets.

As you can see a single query in the database probably won't suffice. If you need some inspiration you can take a look at OSM's address search engine Nominatim. But note that Nominatim uses a different data base scheme than the usual one in order to optimize address queries. You can also take a look at one of the many routing applications which all have to do address lookups.