Check if Street - ZipCode combination exists with OpenStreetMap

for a tool i am programming right now i need to check if certain combinations of zipcode and streetname exists.
After some search i thought that this might be possible with OpenStreetMap. So i downloaded the needed *.osm.bz2 and converted it into an postgre-sql database thanks to osmosis.
But when i am searching through the database for my street-names i often only often only find nodes or ways with the fitting street name as a name-tag but right now i cant see a way to make make a connection between the zip code and the streetname. Except there is a node that has the streetname as tagvalue and the postcode as value.
But somehow it has to be possible to connect street and zip because when i try the search on it can connect the street and the zipcode automatically also for ways, nodes without the needed tags.
Is a direct connection between any given node even the ones without postcode tags and its postalcode with the postgresql possible and i am just to stupid to see it or is that impossible?

Thanks for every answer

Zip codes have not been entered into all of OSM in the US. Zip codes are considered proprietary to the USPS. The main OSM search page uses public sources from GeoNames, which contains an approximation of zip code locations based on TIGER.

As you note, some nodes have had zip codes added where known. In practice, this will be difficult to collect unless there are enough people to define zip code boundaries based on where they live.

so this is going to be a lot more difficult than i thought :slight_smile:

thanks for your answer
regards jonas