update orders set RequiredDate = (case when c.city in ('Seattle','Portland') then date(o.OrderDate) + 1 else date(o.OrderDate) + 2 end)
from orders o
join customers c on
o.Customerid = c.Customerid
where c.region in ('WA','OR')
and orders.orderid = o.orderid
The only difference being that I need to add the join at the end to join the orders table in the update statement with the "orders o" table in the fromlist.
That's because of the explicit join you're using. The "orders o" in the FROM clause is different from the "orders" table in the UPDATE clause.
I'd probably use something like:
UPDATE orders SET RequiredDate = ... FROM customers c WHERE orders.Customerid = c.Customerid AND c.region in (...)
First, does this look correct? It appears to work the way I want. Second, it would be really nice if there was better documentation of the UPDATE statement in Postgres, including examples of this type.
Patches to the documentation are always gratefully received. The latest version of the documentation is available on the main website (follow the developers link). Contributions to the docs mailing-list in plain text are generally fine.
-- Richard Huxton Archonet Ltd
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