ORDER BY not working with UNION ALL

[Cheyenne Forbes <ch...@gmail.com>]

 I get "Undefined column family. familyName=f" whenever I run the following
query,it works without the ORDER BY and works with the ORDER BY if its not
a union and just one select statement

       SELECT
              p.name
        FROM
              person p
        JOIN
              friends f
        ON
              f.person = p.id
        WHERE
              567 != ANY(f.persons)
UNION ALL
        SELECT
              p.name
        FROM
              person p
        JOIN
              friends f
        ON
              f.person = p.id
        WHERE
              123 != ANY(f.persons)
        ORDER BY f.date_time LIMIT 20

Regards,

Cheyenne O. Forbes

Re: ORDER BY not working with UNION ALL

[Sergey Soldatov <se...@gmail.com>]

Well, even if you don't use family, you will get an error that column
date_time is undefined. Consider the result of UNION ALL as a separate
table and ORDER BY is applied to this table. You don't have column
date_time there. Don't forget that UNION ALL may work with different
tables, so there may be no date_time column in the second table.
So you need a construction something like :
select p.name from (select p.name, f.date_time .... UNION ALL select
p.name.f.date_time .... ORDER BY f.date_time LIMIT 20)

Thanks,
Sergey

On Wed, May 3, 2017 at 4:57 PM, Cheyenne Forbes <
cheyenne.osanu.forbes@gmail.com> wrote:

>  I get "Undefined column family. familyName=f" whenever I run the
> following query,it works without the ORDER BY and works with the ORDER BY
> if its not a union and just one select statement
>
>        SELECT
>               p.name
>         FROM
>               person p
>         JOIN
>               friends f
>         ON
>               f.person = p.id
>         WHERE
>               567 != ANY(f.persons)
> UNION ALL
>         SELECT
>               p.name
>         FROM
>               person p
>         JOIN
>               friends f
>         ON
>               f.person = p.id
>         WHERE
>               123 != ANY(f.persons)
>         ORDER BY f.date_time LIMIT 20
>
> Regards,
>
> Cheyenne O. Forbes
>