How to get all houses of street in postgis db?

There is not necessarily a direct link between houses and streets in OSM. The following situations are frequent:

• house is mapped without a street address (addr:street tag) or relation (type=associated_street)
• house has a street address tag
• house is part of an associated_street relation

Unfortunately addr:street tags are not imported by default when you run osm2pgsql; you need to add that column to the config file or import with --hstore. Then you can do something like

SELECT way 
FROM planet_osm_polygon 
WHERE tags->'addr:street'='My Street'

You'll probably also want to check for tags->'addr:city' or for being contained in a certain administrative polygon. Accessing relations is possible when you have used --slim but difficult; it requires looking up the way ID of the house in question in the planet_osm_rels table. A simple alternative is loading all houses in a certain, small distance from a street like

SELECT h.way
FROM planet_osm_polygon h, planet_osm_line s
WHERE s.highway IS NOT NULL and s.name='My Street'
AND ST_DWITHIN(s.way, h.way, 50)

This will of course also find houses belonging to other streets within the specified distance.