Re: Calculation Functions between Columns

On 2004-09-26, Neacal <deb(at)mac(dot)ppc> wrote:
>
> In the O'Reilly book, I can find a number of functions described which
> look like tools for the job, but they are all mentioned as methods to
> SELECT FROM, rather than INSERT INTO. I haven't found anything (so
> far) on columns that can depend on/derive from other columns. Have I
> missed something, or doesn't PostgreSQL do this sort of thing?

What you are describing sounds like a good use for a "view" to me.

Here's an example:

CREATE TABLE sales (
amount int,
quantity int
);

INSERT into sales values (2,3);

CREATE view sub_total as
SELECT (amount * quantity) as subtotal
FROM sales;

SELECT * from sub_total;

subtotal
----------
6

#################

There are more complex solutions as well, such as using triggers to
automatically update the value of one column based on others.

Mark