Codeigniter SUM query brings only one row - database

Question

When I add SUM in Codeigniter SELECT, it returns only one row. But when I remove it, it returns all of the possible matching entries.
$this->db->where('posts.status',1)
->select('posts.title')
->select('posts.description')
->select('posts.posted_by')
->select('posts.posted_on')
->select('posts.category')
->from('posts')
->join('categories','posts.category=categories.id','LEFT')
->select('categories.title as cat_title')
->join('users','users.id=posts.posted_by','LEFT')
->select('users.username')
->select('users.first_name')
->select('users.last_name')
// this section is causing to return only one entry/row,
// when I remove/comment this section, it brings the desired results
->join('votes','votes.post_id=posts.id',"LEFT")
->select('SUM(upvote) as upvote_count')
->select('SUM(downvote) as downvote_count')
->get()
->result_object();

Answer 1

Try to add:
->group_by('posts.id')
After
->select('SUM(downvote) as downvote_count')
So now query will be:
$this->db->where('posts.status',1)
->select('posts.title')
->select('posts.description')
->select('posts.posted_by')
->select('posts.posted_on')
->select('posts.category')
->from('posts')
->join('categories','posts.category=categories.id','LEFT')
->select('categories.title as cat_title')
->join('users','users.id=posts.posted_by','LEFT')
->select('users.username')
->select('users.first_name')
->select('users.last_name')
// this section is causing to return only one entry/row,
// when I remove/comment this section, it brings the desired results
->join('votes','votes.post_id=posts.id',"LEFT")
->select('SUM(upvote) as upvote_count')
->select('SUM(downvote) as downvote_count')
->group_by('posts.id')
->get()
->result_object();