Hi,
I'm currently working with Bernd in an implementation
of updateable views and want to know the hacker's
opinion on this issue.
What features have to be implemented in a first
extension in order to the patch to be accepted? What
features can wait until a second extension?
This are my first thought on this (i start working on
this just two weeks ago).
***************** thoughts *******************
- What if we cannot create one of the three rules?
Make the rule not updateable at all?
Or create the rules we can? (i think this is the
correct)
General Restrictions!!!
---------------------------
- The column target list holds column fields only,
that are retrieved from one base relation / view
only. (NO joined views).
- UNION [ALL]/EXCEPT, DISTINCT and GROUP BY query
expressions aren't updateable at all.
- HAVING, Aggregates, function expressions and
Subqueries aren't allowed to be updateable, too
NOTE: one option is add a catalog that contains info
about updateability of the view attributes, just
like ORACLE's user_updateable_column view
(actually pg_attribute says what columns has a
view, can it be extended?).
That way we can have views in which some columns
are updateable and other are not. Views with
more complicated querys (even joined ones) can
be allowed this way.
Insertable???
----------------------
We need to provide, at least, a value for every column
in the underlaying table that is NOT NULL and do not
have a DEFAULT value.
- If primary key of the table is a serial we can
manage it
CREATE RULE "ins_people_full" as ON
INSERT TO people_full DO INSTEAD
(
INSERT INTO people (person_id, inits, fname)
VALUES (nextval('people_person_id_seq'),NEW.inits,
NEW.fname);
INSERT INTO addresses (person_id,city, state, zip)
VALUES (currval('people_person_id_seq'), NEW.city,
NEW.state, NEW.zip);
);
- What if we add a new not null column without a
default value to the underlaying table? The insert
rule must be deleted?
Updateable???
----------------------
Deleteable???
----------------------
- Can we delete a row from the underlaying table if
the view where i execute the delete stmnt does not
view all the columns in that table?
- What about joined views? What is deleted?
Consider:
CREATE VIEW people_full AS
SELECT p.*, a.city, a.state, s.state_long,
a.country, a.zip
FROM people p JOIN addresses a USING (person_id)
JOIN states s USING (state);
The a.city, a.state, s.state_long, a.country, a.zip
columns must be deleted as well as the p.* columns
***********************************
- Other point is: some people will not be happy
with updateable views, they will want their views to
be read-only. Should we have an extension to the sql
specs for this? Something like a READONLY keyword?
The patch Bernd did, actually covers some of this
points but is just for *very, very* simple views. We
want improve it.
These of course are just general ideas, and we really
want to know your opinion.
regards,
Jaime Casanova
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