Question

我有一张这样的表：

我的表名是：user_viewed_offer

id        user_id      coupon_id
 1           1             65
 2           1             58
 3           1             65
 4           1             65
 5           1             34
 6           1             46
 7           1             24

我想检索这些ID：

4-5-6-7

我使用了group by，但它返回了这些ID：

"[{"id":"7"},{"id":"6"},{"id":"5"},{"id":"2"}]"

我的职能：

$this->db->select('id');
$this->db->from('user_viewed_offer');
$this->db->where('user_id',$user_id);
$this->db->group_by('coupon_id');
$this->db->order_by('id','desc');
$this->db->limit('4');
$data['coupons'] =  $this->db->get()->result();
var_dump(json_encode($data['coupons']));
exit();

我认为我使用distinct语句，但我不知道如何使用它。

Answer 1

将您的表格加入子查询，该子查询为每个优惠券查找每个用户的最新id值。

SELECT t1.id
FROM yourTable t1
INNER JOIN
(
    SELECT user_id, coupon_id, MAX(id) AS max_id
    FROM yourTable
    GROUP BY user_id, coupon_id
) t2
    ON t1.user_id = t2.user_id     AND
       t1.coupon_id = t2.coupon_id AND
       t1.id = t2.max_id
WHERE
    t1.user_id = 1;

Answer 2

似乎你想从coupon_id

中的最大值开始检索id

select id from user_viewed_offer
where id => (
  select max(id)
  from user_viewed_offer 
  where coupon_id  =  (
    select max(coupon_id)
    from user_viewed_offer 
  ) 
)

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2 个答案: