如何从codeigniter中的连接表中获取有限的数据参数？

Hello i want to join three tables but it fetch all data from user table, i just want firstname and lastname parameter in that

Here is my join query. i want something like join(user.firstname).

   $this->db->select('*');
    $this->db->from('post');
    $this->db->join('user', 'user.id = post.cop_id');
    $this->db->join('source', 'post.source_id = source.id');
    $query = $this->db->get();
    return $query->result();

You can do something like this:

$this->db->select('post.*, source.*, user.firstname, user.lastname');
$this->db->from('post');
$this->db->join('user', 'user.id = post.cop_id');
$this->db->join('source', 'post.source_id = source.id');
$query = $this->db->get();
return $query->result();

The table.* indicates that you want all the fields from that table.

change $this->db->select('*'); to $this->db->select('user.firstname, user.lastname');

You can define that in the select:

$this->db->select(['post.id', 'post.title', 'post.description', 'user.firstname']);

Take a look at this answer https://stackoverflow.com/a/15402766/1897484