使用查询工作很好，但由Codeigniter'；s语法不起作用 - using query workding fine but by Codeigniter's syntax not work

using query workding fine but by Codeigniter's syntax not work

以下查询工作正常：

$query = $this->db->query("
    select users.id as user_id ,users.username,traction_details.title,
     traction_details.tr_id,tractions.buy_id,tractions.coupon_code,
     tractions.coupon_property_id,tractions.expired
     from
      users,tractions,traction_details,coupon_cats
        WHERE
          tractions.id = traction_details.tr_id
          AND
          users.id = tractions.user_id
          AND
          coupon_cats.coupon_id = tractions.coupon_parent
          AND
          coupon_cats.cat_id = 13
          AND
          tractions.succ = 1
        GROUP BY tractions.buy_id
        ORDER  BY traction_details.tr_id DESC
        limit
        $start,$end
");
$r = $query->result();
return $r ;

但下面的查询不能正常工作：

   $this->db->select('users.id as user_id');
    $this->db->select('users.username');
    $this->db->select('traction_details.title');
    $this->db->select('traction_details.tr_id');
    $this->db->select('tractions.buy_id');
    $this->db->select('tractions.coupon_code');
    $this->db->select('tractions.coupon_property_id');
    $this->db->select('tractions.expired');

    $this->db->from('users,tractions,traction_details,coupon_cats');

    $this->db->where('tractions.id ' , 'traction_details.tr_id');
    $this->db->where('users.id ' , 'tractions.user_id');
    $this->db->where('coupon_cats.coupon_id ' , 'tractions.coupon_parent');
    $this->db->where('coupon_cats.cat_id =' , '13');
    $this->db->where('tractions.succ =' , '1');
    $this->db->group_by('tractions.buy_id');
    $this->db->order_by('traction_details.tr_id', 'desc');
    $this->db->limit($start, $end);

    $result = $this->db->get()->result();
    return $result;

我的问题在哪里？

您的查询是错误的，不需要重复所有内容。。尝试

$q =
$this->db->select('users.id as user_id ,users.username,traction_details.title,
     traction_details.tr_id,tractions.buy_id,tractions.coupon_code,
     tractions.coupon_property_id,tractions.expired')
    ->from('users,tractions,traction_details,coupon_cats')
    ->where('tractions.id = traction_details.tr_id
          AND
          users.id = tractions.user_id
          AND
          coupon_cats.coupon_id = tractions.coupon_parent
          AND
          coupon_cats.cat_id = 13
          AND
          tractions.succ = 1')
    ->group_by('tractions.buy_id')
    ->order_by('traction_details.tr_id', 'desc')
    ->limit($start, $end)
    ->get();
$result = $q->result();
return $result;

已解决。我将where子句更改为join子句：

$this->db->select('users.id as user_id');
$this->db->select('users.username');
$this->db->select('traction_details.title');
$this->db->select('traction_details.tr_id');
$this->db->select('tractions.buy_id');
$this->db->select('tractions.coupon_code');
$this->db->select('tractions.coupon_property_id');
$this->db->select('tractions.expired');

$this->db->from('tractions');

$this->db->join('traction_details' , 'traction_details.tr_id = tractions.id');
$this->db->join('users' , 'tractions.user_id = users.id');
$this->db->join('coupon_cats' , 'tractions.coupon_parent = coupon_cats.coupon_id');
$this->db->where('coupon_cats.cat_id =' , '13');
$this->db->where('tractions.succ =' , '1');
$this->db->group_by('tractions.buy_id');
$this->db->order_by('traction_details.tr_id', 'desc');
$this->db->limit($start, $end);

$result = $this->db->get()->result();
return $result;