rails query filtering

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 )