Question

我有一个包含以下列的表

编号
ForeignKeyId
的AttributeName
的AttributeValue
创建

部分数据可能如下所示：

1, 1, 'EmailPreference', 'Text', 1/1/2010
2, 1, 'EmailPreference', 'Html', 1/3/2010
3, 1, 'EmailPreference', 'Text', 1/10/2010
4, 2, 'EmailPreference', 'Text', 1/2/2010
5, 2, 'EmailPreference', 'Html', 1/8/2010

我想运行一个查询，为每个不同的ForeignKeyId和AttributeName提取AttributeValue列的最新值，使用Created列确定最近的值。示例输出将是：

ForeignKeyId AttributeName    AttributeValue Created
-------------------------------------------------------
1           'EmailPreference' 'Text'         1/10/2010
2           'EmailPreference' 'Html'         1/8/2010

如何使用SQL Server 2005执行此操作？

Answer 1

单程

select t1.* from (select ForeignKeyId,AttributeName, max(Created) AS MaxCreated
from  YourTable
group by ForeignKeyId,AttributeName) t2
join YourTable t1 on t2.ForeignKeyId = t1.ForeignKeyId
and t2.AttributeName = t1.AttributeName
and t2.MaxCreated = t1.Created

另请参阅Including an Aggregated Column's Related Values了解执行此类查询的5种不同方法

Answer 2

使用：

SELECT x.foreignkeyid,
       x.attributename,
       x.attributevalue,
       x.created
  FROM (SELECT t.foreignkeyid,
               t.attributename,
               t.attributevalue,
               t.created,
               ROW_NUMBER() OVER (PARTITION BY t.foreignkeyid, t.attributename 
                                      ORDER BY t.created DESC) AS rank
          FROM TABLE t) x
 WHERE x.rank = 1

使用CTE：

WITH summary AS (
    SELECT t.foreignkeyid,
           t.attributename,
           t.attributevalue,
           t.created,
           ROW_NUMBER() OVER (PARTITION BY t.foreignkeyid, t.attributename 
                                  ORDER BY t.created DESC) AS rank
      FROM TABLE t)
SELECT x.foreignkeyid,
       x.attributename,
       x.attributevalue,
       x.created
  FROM summary x
 WHERE x.rank = 1

此外：

SELECT t.foreignkeyid,
       t.attributename,
       t.attributevalue,
       t.created
  FROM TABLE t
  JOIN (SELECT x.foreignkeyid,
               x.attributename,
               MAX(x.created) AS max_created
          FROM TABLE x
      GROUP BY x.foreignkeyid, x.attributename) y ON y.foreignkeyid = t.foreignkeyid
                                                 AND y.attributename = t.attributename
                                                 AND y.max_created = t.created

SQL Server仅使用最新值选择不同的行

2 个答案: