Re: Can I do this smarter?

Aaron Bono wrote:

> On 7/13/06, *Joost Kraaijeveld* <J(dot)Kraaijeveld(at)askesis(dot)nl
> <mailto:J(dot)Kraaijeveld(at)askesis(dot)nl>> wrote:
>
> I have three tables: customers, salesorders and invoices.
> Customers have
> salesorders and salesorders have invoices ( child tables have foreign
> key columns to their parent).
>
> I want to get a list of all invoices with their customers. This
> what I
> came up with:
>
> select
> invoices.objectid,
> invoices.invoicenumber,
> invoices.invoicedate,
> (select customer from salesorders where objectid =
> invoices.salesorderobjectid),
> (select customernumber from customers where objectid = (select
> customer from salesorders where objectid =
> invoices.salesorderobjectid)),
> (select lastname from customers where objectid = (select customer
> from salesorders where objectid = invoices.salesorderobjectid))
> from invoices
>
> Can I do this smarter as the three subselects select the same
> customer three times and I would think that 1 time is enough?
>
>
>
> SELECT
> invoices.objectid,
> invoices.invoicenumber,
> invoices.invoicedate,
> salesorders.customer,
> customers.customernumber,
> customers.lastname
> FROM invoices
> INNER JOIN salesorders ON (
> salesorders.objectid = invoices.salesorderobjectid
> )
> INNER JOIN customers ON (
> customers.objectid = salesorder.customer
> )
>
> You should do INNER and OUTER joins for connecting the tables by
> their foreign keys.

You can also rewirite this (IMO) more clearly thus:

SELECT
invoices.objectid,
invoices.invoicenumber,
invoices.invoicedate,
salesorders.customer,
customers.customernumber,
customers.lastname
FROM invoices, salesorders, customers
WHERE salesorders.objectid = invoices.salesorderobjectid
AND customers.objectid = salesorder.customer;

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Aaron Bingham
Senior Software Engineer
Cenix BioScience GmbH
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