Subject: Re: [GENERAL] 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
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