選擇警報類型和項目標識相同的行，並選擇多少行類似

Question

我試圖在我的項目中儘可能簡化通知系統。

「約翰·布朗和另外4人喜歡你的照片」

我想：

Select a.id, a.item_id, a.type u.f_name, u.l_name, count(a) 
From alerts 
Join users on a.user_id = u.u_id 
Where owner_id = {THE_USER_ID} 

但它不 「工作」

---

用戶表

u_id | f_name | l_name 
========================== 
234 roy  wright  
654 pam  brown 
564 kim  harris 
334 tory  plummer 
876 rick  forbes  
123 paul  nichol 
980 mario chang 
454 todd  thompson 
886 sam  richards 
215 tash  gates 
... ..... ........ 

警報表

id | item_id | type | user_id | owner_id 
=================================================== 
1   21   like  234 
2   21   comment 654 
3   32   share  876 
4   21   like  778 
5   21   like  890 
6   21   share  123 
7   54   share  454 
8   32   comment 655 
9   60   comment 886 
10  32   like  215 
..  ..   ...... ... 

結果我想

id | item_id | type | u_id | f_name | l_name | amount_more 
============================================================ 
1 21  like  234 roy  wright 2 
2 21  comment 654 pam  brown 
3 32  comment 876 rick  forbes  
6 21  share 123 paul  nichol 
7 54  share 454 todd  thompson 
9 60  comment 886 sam  richards 
10 32  like  215 tash  gates 
.. ..  ....  ... ..... ........ 

Answer 1

SELECT 
    MIN(CASE WHEN RowNumber = 1 THEN id END) as Id 
    ,item_id 
    ,type 
    ,MIN(CASE WHEN RowNumber = 1 THEN u_id END) as u_id 
    ,MIN(CASE WHEN RowNumber = 1 THEN f_name END) as f_name 
    ,MIN(CASE WHEN RowNumber = 1 THEN l_name END) as l_name 
    ,COUNT(*) - 1 as amount_more 
FROM 
    (
    SELECT 
     t.* 
     ,(@rn:= if((@item = t.item_id) AND (@type = t.type),@rn + 1, 
        if((@item:=t.item_id) AND (@type:=t.type),1,1) 
      ) 
     ) as RowNumber 
    FROM 
     (SELECT * 
     FROM 
      alerts a 
      LEFT JOIN usersTbl u 
      ON a.user_id = u.u_id 
     WHERE 
      a.owner_id = 201 
     ORDER BY 
      a.item_id 
      ,a.type 
      ,a.id) t 
     CROSS JOIN (SELECT @rn:=0,@item:=0,@type:='') var 
    ORDER BY 
     item_id 
     ,type 
     ,id 
    ) t2   
GROUP BY 
    item_id 
    ,type 
ORDER BY 
    id 
;  

所以，你需要創建一個分區的行號來確定首先考慮哪個記錄。然後使用條件聚合，你可以選擇你的用戶。這個工作在這裏檢查：http://rextester.com/VXZONO82847

Answer 2

在查詢您沒有使用別名A和U得當，使用此：

Select 
a.id, 
a.item_id, 
a.type, 
u.f_name, 
u.l_name, 
count(a.*) 
From alerts a Join users u 
on(a.user_id = u.u_id) 
Where owner_id = {THE_USER_ID} 
group by 1,2,3,4,5;