SQL SELECT两者之间由日期

Question

加入我有两个表： 1-设置

EffectiveDate ||  Value 
============================== 
'2000-01-01' ||  2 
'2005-01-01' ||  4 
'2010-01-01' ||  6 

2- DataTable中

 ID  || RecordDate 
=============================== 
     1  || '2001-01-01' 
     2  || '2002-01-01' 
     3  || '2003-01-01' 
     4  || '2007-01-01' 
     5  || '2008-01-01' 
     6  || '2011-01-01' 
     7  || '2013-01-01' 
     8  || '2014-01-01' 

这两个表之间的关系是，从EffectiveDate从Settings most be smaller(and/or equal) than RecordDateDataTable但必须是最新的。 例如其结果必然是这样的：

 ID  || RecordDate || value 
======================================== 
     1  || '2001-01-01' || 2 
     2  || '2002-01-01' || 2 
     3  || '2003-01-01' || 2 
     4  || '2007-01-01' || 4 
     5  || '2008-01-01' || 4 
     6  || '2011-01-01' || 6 
     7  || '2013-01-01' || 6 
     8  || '2014-01-01' || 6 

感谢您的帮助：d

Answer 1

您可以使用CROSS APPLY和TOP以达到预期的效果：

SELECT 
    dt.ID, dt.RecordDate, x.Value 
FROM DataTable dt 
CROSS APPLY(
    SELECT TOP 1 Value 
    FROM Settings s 
    WHERE s.EffectiveDate <= dt.RecordDate 
    ORDER BY s.EffectiveDate DESC 
) x 

ONLINE DEMO