Question

我正在努力使用户项目的通知系统尽可能简单。

＆＃34;约翰·布朗和另外4人喜欢你的照片＆＃34;

我试过了：

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}

但它没有＆＃34;工作＆＃34;

用户表

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
...    .....    ........

警报表

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
..        ..           ......    ...

我想要的结果

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
;

因此，您需要创建一个分区行号，以识别您想要首先考虑的记录。然后使用条件聚合，您可以选择它作为您的用户。这可以在这里查看：http://rextester.com/VXZONO82847

Answer 2

在查询中，您没有正确使用别名a和u，请使用此：

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;

选择警报类型和项目ID相同的行以及相似的行数

2 个答案: