List primary keys for all tables - Postgresql

This is more accurate answer:

select tc.table_schema, tc.table_name, kc.column_name 
from  
    information_schema.table_constraints tc,  
    information_schema.key_column_usage kc  
where 
    tc.constraint_type = 'PRIMARY KEY' 
    and kc.table_name = tc.table_name and kc.table_schema = tc.table_schema
    and kc.constraint_name = tc.constraint_name
order by 1, 2;

You missed the and kc.constraint_name = tc.constraint_name part, so it lists all constraints.

Something like this:

select tc.table_schema, tc.table_name, kc.column_name
from information_schema.table_constraints tc
  join information_schema.key_column_usage kc 
    on kc.table_name = tc.table_name and kc.table_schema = tc.table_schema and kc.constraint_name = tc.constraint_name
where tc.constraint_type = 'PRIMARY KEY'
  and kc.ordinal_position is not null
order by tc.table_schema,
         tc.table_name,
         kc.position_in_unique_constraint;