I have already loaded osm data into postgresql earlier. Now I want to update the database. I have downloaded the pbf file from geofabrik. How I can update the database without deleting the existing Tables?
If you have imported a planet or extract some time ago and have now downloaded a (much) newer planet or extract:
It does not really make sense to do any updating as I think calculating and applying the diff will not save you time. Just re-run osm2pgsql again and it will remove the tables and create new ones resulting in updated data.
If you want to keep your data updated continuously:
Download diff files provided by different providers (e.g. Geofabrik), see Planet.osm/diffs for more information. Then use e.g. Osmosis in combination with
osm2pgsql --append. Switch2OSM with section "Updating" might also provide hints.