两个表之间的SQL SELECT按日期连接

Question

我有两张桌子： 1-设置

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

2- DataTable

      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'

这两个表格之间的关系是来自EffectiveDate的{​​{1}} Settings most be smaller(and/or equal) than RecordDate，但必须是最新的。{1}}。 例如，结果必须是这样的：

DataTable

谢谢你的帮助：D

Answer 1

您可以使用CROSS APPLY和TOP来获得所需的结果：

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