Re: Column as result of subtraction of two other columns?

Try

select a, b, (b - a) as diff from (
select 1 as a, 2 as b
) as tmp;

John Sidney-Woollett

Bruno Wolff III wrote:

> On Fri, Jul 16, 2004 at 15:31:33 +0100,
> Mark Cave-Ayland <m(dot)cave-ayland(at)webbased(dot)co(dot)uk> wrote:
>
>>Hi everyone,
>>
>>I'm trying to calculate an output column which is the difference of two
>>other columns in the query output; the first column is an aggregate of
>>items in stock, while the second column is an aggregate of items which
>>have been used. The third column should should be the difference of the
>>two values so I can then output all three columns in a table.
>>
>>Unfortunately I can't get this to work at the moment :(. I've simplified
>>the query down to the following:
>>
>>dev=# select 1 as a, 2 as b, (b - a) as c;
>>ERROR: column "b" does not exist
>>dev=#
>>
>>Do I need to create some form of alias so the calculation can see the
>>other columns? I am using PostgreSQL 7.4.2 on Linux.
>
>
> You can't use column aliases in other columns; you need to repeat the
> column expressions.
>
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