Re: ambiguous

On Wed, 7 Mar 2001, si wrote:

> If I assign the same name to 2 columns in 2 different tables:
>
> +--------------------------------------+
> |              DEPARTMENT              |
> +----------+----------------+----------+
> | LOCATION |  DESCRIPTION   |  DEPT_NO |
> +----------+----------------+----------+
> | Bedrock  | Administration |     1    |
> +----------+----------------+----------+
>
> +--------------------------------+
> |            EMPLOYEE            |
> +---------+------------+---------+
> | EMPL_ID | NAME_LAST  | DEPT_NO |
> +---------+------------+---------+
> |    1    | Slate      |     1   |
> +---------+------------+---------+
>
> select * from DEPARTMENT, Employee where dept_no = '1';
>
> PG throws up:
> ERROR:  Column 'dept_no' is ambiguous
>
> Is this not allowed? or is my sql understanding wrong?

It's correct behavior, because it can't differentiate between the two
fields with the same name.  But this shouldn't present a problem if you
are using dept_no as a join field.  You will want to select things this
way:

select d.*, e.empl_no, d.name_last from DEPARTMENT d, Employee e where
e.dept_no = d.dept_no and d.dept_no = 1;

It's longer SQL, but it's also more precise.

-- Brett
                http://www.chapelperilous.net/~bmccoy/
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