count with group by discards :distinct option

I am not fully sure what value distint will bring in this case since grouping is always by same vlaue.

In this case I have three cars with names: honda, toyota and toyota.

ree-1.8.7-2010.02 > Car.group(:name).count(:name, :distinct => true)
  SQL (0.3ms)  SELECT COUNT("r_cars"."name") AS count_name, name AS name FROM "r_cars" GROUP BY name
 => #<OrderedHash {"honda"=>1, "toyota"=>2}>

By distinct you mean the count for toyota should be '1' ?

Here is an example: I have posts published by users, and I want to know how many different users are publishing posts everyday.

Post.create(:user_id => 1, :created_on => '2010-09-29')
Post.create(:user_id => 1, :created_on => '2010-09-29')
Post.create(:user_id => 2, :created_on => '2010-09-29')
Post.create(:user_id => null, :created_on => '2010-09-29')

Post.group(:created_on).count)
# => {'2010-09-29' => 4}

Post.group(:created_on).count(:user_id)
# => {'2010-09-29' => 3}

Post.group(:created_on).count(:user_id, :distinct => true)
# => {'2010-09-29' => 2}

From the MySQL documentation:

• COUNT(*) counts the total number of rows.
• COUNT(column) counts rows with non null column.
• COUNT(DISTINCT column) counts rows with different, non null column.

(from [1c9022de212c190362d40b98624dcf71d20ca073]) Honor distinct option when used with count operation after group clause [#5721 count with group by discards :distinct option state:resolved] http://github.com/rails/rails/commit/1c9022de212c190362d40b98624dcf...