Re: Can I do this smarter?

Aaron Bono wrote:

> On 7/13/06, *Joost Kraaijeveld* <J.Kraaijeveld@askesis.nl 
> <mailto:J.Kraaijeveld@askesis.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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