Rails query filtering

Rails
1

I am trying to set up a filter form, in which I can select users based
on User attributes and get a count of the user’s post filtered on Post
attributes

this generated query runs very well,

SELECT DISTINCT users.* FROM users LEFT OUTER JOIN posts ON
posts.user_id = users.id WHERE (posts.title LIKE ‘%pa%’)
ORDER BY users.last_name ASC

and I can display all selected users info :
%tr
%td= user.id
%td= user.first_name
%td= user.last_name
%td= user.email

but how can I add a column with the number of filtered posts for each
user ?

thanks for your feedback [using Rails 3.2.3 )