Re: select a list of column values directly into an array

On Tue, Jul 27, 2010 at 9:03 AM, Gauthier, Dave <dave.gauthier@intel.com> wrote:
> Is there a way to select a list of column values directly into an array?
>
> create table foo (col1 text);
>
> insert into foo (col1) values (‘aaa’),(‘bbb’),(‘ccc’),(‘ddd’),(‘eee’);
>
> I’d like to load up an array with {aaa,bbb,ccc,ddd,eee}, prefferably with a
> single select statement.

There are basically four ways to create an array:

*) text in:
select '{1,2,3,4,5}'::int[];

obviously not the best method: use it for example when you need to
parameterize a query from a client that doesn't understand pgsql
natives natively (which is basically all of them).

*) list of scalars:
select array[1,2,3,4,5];

use that when you have a known list of constants you want of feed to a
query.  better version of the above, but it can be awkward if you
parameterize your queries

*) array syntax construct
select array(select col from foo);

takes the result of any query and arrayifies it.  you can also 'stack'
arrays, even using full types:

select array
(
  select row
  (
    foo,
    (
      array(select bar from bar where bar.foo_id = foo.foo_id)
    )
  )  from foo
);

it's advisable to use declared composite types when doing really fancy
stuff with this...

*) array_agg

aggregates a column 'in query' using grouping rules. I would only
advise this when you want to make use of 'group by'.

merlin