Re: Chaining inserts ... This would be cool

On 23 April 2012 21:49, Nick Apperson <apperson@gmail.com> wrote:
> There are obviously workarounds for this, but I'm wondering why the
> following query shouldn't work. It seems like it should. With MVCC already
> present on the back-end, I can't see any reason other than additional
> parsing routines that this couldn't work:
>
> INSERT INTO old_login_id_to_new_account_id(new_account_id, old_login_id)
> INSERT INTO accounts(id, username, password_hash, email) SELECT DEFAULT,
> username, password_hash, email FROM logins_old RETURNING id, logins_old.id;
>
> Anyway, I'm sure there are more important features for Postgres (like
> upserts, unique indexes on GIN, Gist and hash, fixed arrays, compact storage
> of enum arrays as bitfields, etc.) I just thought it was an interesting
> idea.

You should be able to use writeable common table expressions to
achieve a linking behaviour.

http://www.postgresql.org/docs/9.1/static/queries-with.html
http://www.depesz.com/index.php/2011/03/16/waiting-for-9-1-writable-cte/
http://thombrown.blogspot.de/2011/11/writeable-common-table-expressions.html

But I'm not sure the query you posted makes any sense.  Why would a
SELECT statement have a RETURNING clause?  And where do the values for
the first INSERT come from?
--
Thom