Codeigniter：获取相同值之间的公共列值

I have the following table

id    group_id   user_id
1     2          11
2     2          12
3     2          13
4     3          11
5     3          12
6     4          11

Now I want the common group IDs Means if

I pass user_id (11,12) then result will be group_id (2 and 3)
I pass user_id (11) then result will be group_id (2,3 and 4)
I pass user_id (11,12,13) then result will be group_id (2)
I pass user_id (13,15) then result will be zero group_id (NULL)

I am working with CodeIgniter but you can suggestion me in core SQL. It would be good if your answer is in CI model(query) standard.

You can use distinct and where_in to get your desire result. Where array contain your user_id

$this->db->distinct();
$this->db->select('group_id');
$this->db->from('your_table');
$this->db->where_in('user_id',array('11','12');//you can pass here 11,12,13 or 11 or 11,12

For And Condition

$array = array('user_id' => 11, 'user_id' => 12);

    $this->db->distinct();
    $this->db->select('group_id');
    $this->db->from('your_table');
    $this->db->where($array);

One way to do it is to use the NATURAL JOIN of SQL.

For user_id = 11

SELECT group_id FROM table_name WHERE user_id = 11;

For user_id = 11,12

SELECT group_id FROM 
    (SELECT group_id FROM table_name WHERE user_id = 11) t1 
        NATURAL JOIN 
    (SELECT group_id FROM table_name WHERE user_id = 12) t2;

For user_id = 11,12,13

SELECT group_id FROM 
    (SELECT group_id FROM table_name WHERE user_id = 11) t1 
        NATURAL JOIN 
    (SELECT group_id FROM table_name WHERE user_id = 12) t2 
        NATURAL JOIN 
    (SELECT group_id FROM table_name WHERE user_id = 13) t3;

SELECT *, group_concat(DISTINCT(group_id)) FROM test_temp WHERE user_id IN(11,12)