不同/連接兩個表

Question

商店表：

+--+-------+--------+ 
    |id|name |date | 
    +--+-------+--------+ 
    |1 |x  |March 10| 
    +--+-------+--------+ 
    |2 |y  |March 10| 
    +--+-------+--------+ 

類別表：

+--+-------+ 
|id|title | 
+--+-------+ 
|1 |tools | 
+--+-------+ 
|2 |foods | 
+--+-------+ 

店類別表（shop_cats）：

+--+-------+--------+ 
|id|shop_id|cat_id | 
+--+-------+--------+ 
|1 |1  |1  | 
+--+-------+--------+ 
|2 |1  |2  | 
+--+-------+--------+ 

我想按類別商店（類別存儲在$ cat數組中）

 $this->db->select('shops.*'); 
    $this->db->from('shops'); 
    if(!empty($cat)) 
    { 
     $this->db->join('shop_cats' , 'shop_cats.shop_id = shops.id'); 
     $this->db->where_in('shop_cats.cat_id' , $cat); 
    } 


    $this->db->limit($limit , $offset); 
    $res = $this->db->get(); 

我的問題是，它返回重複的結果 例如，在該表中

+--+-------+--------+ 
|id|shop_id|cat_id | 
+--+-------+--------+ 
|1 |1  |1  | 
+--+-------+--------+ 
|2 |1  |2  | 
+--+-------+--------+ 

，如果我想用（1,2）I類獲得ID = 1號店的商店，兩次。 我希望它只返回每個商店一次而沒有任何重複。

我已經嘗試過通過

if(!empty($cat)) 
     { 
      $this->db->join('shop_cats' , 'shop_cats.shop_id = shops.id'); 
      $this->db->group_by('shop_cats.shop_id'); 
      $this->db->where_in('shop_cats.cat_id' , $cat); 
     } 

使用組也沒有工作，我也試着

if(!empty($cat)) 
     {   $this->db->select('DISTINCT shop_cats.shop_id'); 
      $this->db->join('shop_cats' , 'shop_cats.shop_id = shops.id'); 
      $this->db->where_in('shop_cats.cat_id' , $cat); 
     } 

，但我得到語法錯誤！

Answer 1

嘗試

$this->db->distinct('shops.*'); 
$this->db->from('shops'); 
$this->db->join('shop_cats', 'shop_cats.shop_id = shops.id', 'left'); 
$this->db->where('shop_cats.cat_id', $cat); 
$this->db->limit($limit , $offset); 
$res = $this->db->get();