title: concat in mysql using codeigniter
body: <p>In my application every user can like every comment.But each like is entered as comma seperated form.User id of each users like entered into database as 2,4,5..etc.I use concat in my model like this</p>
  
  <pre><code>        public function shop_like($shop_id,$user_id,$logged_id)
          { 
              $this-&gt;db-&gt;where('user_id',$user_id);
  
              $this-&gt;db-&gt;where('shop_id', $shop_id);
              $this-&gt;db-&gt;set('review_like', 'review_like+1', FALSE);
              $where = "CONCAT('like_user_id', ',','".$logged_id."')"; 
             // $where = CONCAT(like_user_id,'".$logged_id."');
              $this-&gt;db-&gt;set('like_user_id', $where);
              $this-&gt;db-&gt;set('review_like', 'review_like+1', FALSE);
              $this-&gt;db-&gt;update('shop_reviews',$data);
            }
  </code></pre>
  
  <p>Each like, the like_user_id field contain the inserted value like this CONCAT(like_user_id, ',','7') this is the problem</p>
  
  <p>I want the existing comma seperated values and the user id of liked user</p>
  
  <p>plzz correct the syntax of concat</p>