gwow_dev_renchap=# select version();
                                                      version
--------------------------------------------------------------------------------------------------------------------
 PostgreSQL 8.2.6 on x86_64-pc-linux-gnu, compiled by GCC x86_64-pc-linux-gnu-gcc (GCC) 4.1.2 (Gentoo 4.1.2 p1.0.2)
(1 row)

gwow_dev_renchap=# select get_site_id();
 get_site_id
-------------
           1
(1 row)

gwow_dev_renchap=# \df+ get_default_value;
                                                                                                                   List of functions
 Schema |       Name        |         Result data type          |                Argument data types                |  Owner  | Language | Source code                                          | Description
--------+-------------------+-----------------------------------+---------------------------------------------------+---------+----------+-----------------------------------------------------------------------------------------------+-------------
 public | get_default_value | information_schema.character_data | table character varying, column character varying | renchap | sql      | SELECT column_default FROM information_schema.columns WHERE table_name=$1 AND column_name=$2; |
(1 row)

gwow_dev_renchap=# \d zf_categories
                                    Table "public.zf_categories"
    Column     |         Type          |                         Modifiers
---------------+-----------------------+------------------------------------------------------------
 id            | integer               | not null default nextval('zf_categories_id_seq'::regclass)
 cat_name      | character varying(80) | not null default 'New Category'::character varying
 disp_position | integer               | not null default 0
 site_id       | integer               |
Indexes:
    "zf_categories_pkey" PRIMARY KEY, btree (id)
    "zf_categories_site_id" btree (site_id)
    "zf_categories_site_id_idx" btree (site_id)

gwow_dev_renchap=# \d z_categories
            View "public.z_categories"
    Column     |         Type          | Modifiers
---------------+-----------------------+-----------
 id            | integer               |
 cat_name      | character varying(80) |
 disp_position | integer               |
View definition:
 SELECT zf_categories.id, zf_categories.cat_name, zf_categories.disp_position
   FROM zf_categories
  WHERE zf_categories.site_id = get_site_id();
Rules:
 delete_z_categories AS
    ON DELETE TO z_categories DO INSTEAD  DELETE FROM zf_categories
  WHERE zf_categories.id = old.id AND zf_categories.site_id = get_site_id()
 insert_z_categories AS
    ON INSERT TO z_categories DO INSTEAD  INSERT INTO zf_categories (site_id, cat_name, disp_position)
  VALUES (get_site_id(), COALESCE(new.cat_name, get_default_value('zf_categories'::character varying, 'cat_name'::character varying)::character varying), COALESCE(new.disp_position, get_default_value('zf_categories'::character varying, 'disp_position'::character varying)::integer))
 update_z_categories AS
    ON UPDATE TO z_categories DO INSTEAD  UPDATE zf_categories SET id = new.id, cat_name = new.cat_name, disp_position = new.disp_position
  WHERE zf_categories.id = old.id AND zf_categories.site_id = get_site_id()

gwow_dev_renchap=# SELECT * FROM zf_categories ORDER BY id;
 id |   cat_name    | disp_position | site_id
----+---------------+---------------+---------
  1 | Test category |             1 |       2
  2 | new cat 3     |             0 |       2
(2 rows)

gwow_dev_renchap=# INSERT INTO z_categories (cat_name, disp_position) VALUES ('My Cat', 5);
INSERT 0 1
gwow_dev_renchap=# SELECT * FROM zf_categories ORDER BY id;
 id |   cat_name    | disp_position | site_id
----+---------------+---------------+---------
  1 | Test category |             1 |       2
  2 | new cat 3     |             0 |       2
 22 | My Cat        |             5 |       1
(3 rows)

gwow_dev_renchap=# INSERT INTO z_categories (cat_name) VALUES ('My New Cat');
INSERT 0 1
gwow_dev_renchap=# SELECT * FROM zf_categories ORDER BY id;
 id |   cat_name    | disp_position | site_id
----+---------------+---------------+---------
  1 | Test category |             1 |       2
  2 | new cat 3     |             0 |       2
 22 | My Cat        |             5 |       1
 23 | My New Cat    |             0 |       1
(4 rows)

gwow_dev_renchap=# UPDATE z_categories SET disp_position=2;
UPDATE 2
gwow_dev_renchap=# SELECT * FROM zf_categories ORDER BY id;
 id |   cat_name    | disp_position | site_id
----+---------------+---------------+---------
  1 | Test category |             1 |       2
  2 | new cat 3     |             0 |       2
 22 | My Cat        |             2 |       1
 23 | My New Cat    |             2 |       1
(4 rows)

gwow_dev_renchap=# UPDATE z_categories SET disp_position=2 WHERE id=1;
UPDATE 0

gwow_dev_renchap=# SELECT * FROM z_categories ORDER BY id;
 id |  cat_name  | disp_position
----+------------+---------------
 22 | My Cat     |             2
 23 | My New Cat |             2
(2 rows)

gwow_dev_renchap=# DELETE FROM z_categories WHERE id = 23;
DELETE 1
gwow_dev_renchap=# SELECT * FROM zf_categories ORDER BY id;
 id |   cat_name    | disp_position | site_id
----+---------------+---------------+---------
  1 | Test category |             1 |       2
  2 | new cat 3     |             0 |       2
 22 | My Cat        |             2 |       1
(3 rows)

gwow_dev_renchap=# DELETE FROM z_categories;
DELETE 1
gwow_dev_renchap=# SELECT * FROM zf_categories ORDER BY id;
 id |   cat_name    | disp_position | site_id
----+---------------+---------------+---------
  1 | Test category |             1 |       2
  2 | new cat 3     |             0 |       2
(2 rows)