Re: Column "..." does not exist (view + union)

On Saturday, December 17, 2011 2:21:30 pm Stefan Weiss wrote:

> 
> I know, but the problem only occurs when I want to sort by a column
> which hasn't been selected, and thus cannot be referred to by its index.
> For normal (non-union) queries, this is possible:
> 
>     SELECT relname
>       FROM pg_class
>      WHERE relhasindex
>   ORDER BY relpages;
> 
> In this trivial case, PostgreSQL knows where to look for "relpages".
> Not so in a union:
> 
>     SELECT relname
>       FROM pg_class
>      WHERE relhasindex
> UNION
>     SELECT relname
>       FROM pg_class
>      WHERE relhasoids
> ORDER BY relpages;
> 
> (ERROR: column "relpages" does not exist)
> 
> I understand the error now (I think), and I know how to avoid it.


SELECT relname     FROM pg_class    WHERE relhasindex
UNION   (SELECT relname     FROM pg_class    WHERE relhasoids    ORDER BY relpages);


> 
> 
> thanks,
> stefan

-- 
Adrian Klaver
adrian.klaver@gmail.com