select distinct returns nil (globalize3)

Post.find(:all, :select => "DISTINCT author")

returns

[#<Post author: nil>, #<Post author: nil>, #<Post author: nil>, #<Post author: nil>, #<Post author: nil>].

However SQL request SELECT DISTINCT author FROM posts; works as expected.

I'm using globalize3. Post.select('DISTINCT author').with_translations('en') returns all records.

Here is it's log:

Post Load (0.5ms)  SELECT "posts"."id" AS t0_r0, "posts"."description" AS t0_r1, "posts"."position" AS t0_r2, "posts"."created_at" AS t0_r3, "posts".开发者_如何学C"updated_at" AS t0_r4, "posts"."date" 
AS t0_r5, "post_translations"."id" AS t1_r0, "post_translations"."post_id" AS t1_r1, "post_translations"."locale" AS t1_r2, "post_translations"."author" 
AS t1_r3, "post_translations"."description" AS t1_r4, "post_translations"."created_at" AS t1_r5, "post_translations"."updated_at" 
AS t1_r6 FROM "posts" LEFT OUTER JOIN "post_translations" ON "post_translations"."post_id" = "posts"."id" WHERE "post_translations"."locale" = 'en' 
AND (post_translations.author IS NOT NULL)

How can I select only distinct values?

Might be this simple:

Post.find(:all, :group => author)

Update:

Looks like postgres is a little more compliant than mysql, so try this instead:

Post.select("DISTINCT ON (author) *")