some error of using osm2pgsql to import .osm data to PostgreSQL

General talk
1

Hi people!
I’m a novice!

   after  I  used osm2pgsql to import .osm data to PostgreSQL, I found tables(planet_osm_line/points/polygon/roads) haves no primary key.

    and, the command I used like this and it ran all ok : 

    osm2pgsql -U postgres -d osmdb2 -k -s -S ./default.style ./beijing_china.osm

  what do you think?
  thanks.