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

On Tue, Aug 2, 2016 at 2:17 PM, Kevin Grittner <kgrittn@gmail.com> wrote:

On Tue, Aug 2, 2016 at 11:48 AM, David Muller <dmuller@guidebook.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