根据表字段对数据进行分组

Question

我有以下表格：

BarcodeGroupMap：

正如我们在“组”字段中看到的，根据其EffectFrom日期，我有不同的组和barcodeItem。

我只想根据群组对条形码项目进行分组，但对于相同的条形码项目，它应该考虑最近/最大效果从日期开始。

输出我的愿望：

Group  BarcodeItem   EffectFrom
1           1          2013-11-10
1           11        2013-11-14
1           22        2013-11-10 (max date amount 3 for barcode item 22)
1          222        2013-11-14
1          333        2013-11-14 
1         3331        2013-11-14 

我做了以下查询：

select * from BarcodeGroupMap bm ,

 ( 
  select groups,barcodeitem,bcgmid ,MAX(EffectFrom) as dates,CreatedDate as cdate from BarcodeGroupMap 
  group by groups ,barcodeitem,bcgmid,CreatedDate  having Groups=1 

 ) T 
 where t.Groups =bm.Groups and t.BarcodeItem = bm.BarcodeItem and  T.Groups =  1 and t.dates =bm.EffectFrom  Order by t.BarcodeItem , t.Groups

但不工作。请帮帮我。

Answer 1

select groups as [group], barcodeitem, max(EffectFrom) as EffectFrom
from BarcodeGroupMap 
group by groups, barcodeitem
order by groups, barcodeitem

Answer 2

<强>已更新

SELECT * 
  FROM
(
    SELECT m.*, ROW_NUMBER() OVER (PARTITION BY groups, barcodeitem 
                                   ORDER BY effectfrom DESC, createddate DESC) rnum
      FROM BarcodeGroupMap m
     WHERE groups = 1
) t
 WHERE rnum = 1
 ORDER BY groups, barcode item

这是 SQLFiddle 演示