Re: Column Does Not Exist Error: Order by an Particular Cell of an Array

On Tue, Aug 2, 2016 at 11:48 AM, David Muller <dmuller(at)guidebook(dot)com> wrote:

> gears=> select *, Array[4,5] as array_from_select from foo order by
> array_from_select[1];
>
> ERROR: column "array_from_select" does not exist

array_from_select is not a column name, it is an alias. The ways
in which an alias can be used in a query are somewhat limited --
you can order by the alias of a result column, but you can't use
the alias in arbitrary expressions.

You could do something like this:

test=# with x as (select *, Array[4,5] as array_from_select from foo)
test-# select * from x order by array_from_select[1];
value | array_from_select
-------+-------------------
1 | {4,5}
2 | {4,5}
(2 rows)

In this case array_from_select becomes a column in the result set
of common table expression (CTE) x and *can* be used in
expressions.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company