ruby - Remove duplicated records based on pair of columns? -

i have table folowwing columns:

id app_id tag_id created_at updated_at 

the pair app_id , tag_id should uniq. how remove oldest duplicated records based on updated_at column determine "oldest" , pair (app_id, tag_id) determine "duplicated"?

 activerecord::base.connection.execute <<-sql    delete my_table id in (      select t1.id      my_table t1      inner join (        select app_id, tag_id, min(updated_at) oldest        my_table        group app_id, tag_id      ) t2       on t1.app_id = t2.app_id       , t1.tag_id = t2.tag_id      , t1.updated_at = t2.oldest    )  sql 

replace my_table actual table name.