我会推荐这个官方版本：

http://wiki.postgresql.org/wiki/Retrieve_primary_key_columns

如果需要模式，查询如下

SELECT               
  pg_attribute.attname,format_type(pg_attribute.atttypid,pg_attribute.atttypmod) 
FROM pg_index,pg_class,pg_attribute,pg_namespace 
WHERE 
  pg_class.oid = 'foo'::regclass AND 
  indrelid = pg_class.oid AND 
  nspname = 'public' AND 
  pg_class.relnamespace = pg_namespace.oid AND 
  pg_attribute.attrelid = pg_class.oid AND 
  pg_attribute.attnum = any(pg_index.indkey)
 AND indisprimary