选择SQL连接语句上一对多关系的最上面匹配记录

Question

我有一个问题，可能会很简单，但无论如何我都不是SQL专家。 我的查询具有3个联接，第3个是一对多关系，并且我试图获得前1个。在这种情况下，这将是对支持电话的最后一次编辑。

该信息来自4个表，其中CASE用于基本案例详细信息，CONTACT1和CONTACT2用于联系信息，以及该案例注释的NOTES，该NOTES表为在这种情况下输入的每个注释创建1个条目。 我想创建一个仪表板，其中将包含最后一个输入时间戳。

我试图在联接中添加一个选择顶部（1），尝试了联接的所有可能选项，并将Max（C3.MODIFIEDDATE）与Group By一起使用，但是我总是以每张票证中NOTES的所有记录为最终结果。

这是我的查询：

SELECT c.NUMBER as [Case Number], c.OWNER as [Assigned To], case c.status when 0 then '<unknown>' when 1 then 'Assigned' when 2 then 'Reassigned' when 3 then 'Escalated' when 4 then 'Resolved' 
else cast(c.status as varchar(50)) end as [Case Status], c.SUBJECT as [Subject], c.OFFERING as [Next Step], DATEADD(day,DATEDIFF(day,0,c.CREATED_DATE),0) as [Created on], c1.CONTACT 
as [Primary Contact], c1.COMPANY as [Company], c3.MODIFIEDDATE as [Last Edit], c3.MODIFIEDBY as [Last Agent]

FROM CASES c left join(CONTACT1 c1 inner join CONTACT2 c2 on c1.ACCOUNTNO = c2.ACCOUNTNO ) on c1.ACCOUNTNO = c.ACCOUNTNO 
   left join NOTES as c3 on c3.LOPRECID =c.recid -- That's the one that has a 1 to many resolve


WHERE (  c.IS_TEMPLATE = 0  AND   c.STATUS IN ( 1,2,3 ) and c3.rectype='CS' )
ORDER BY [Company] asc, c3.modifieddate desc

任何建议将不胜感激

Answer 1

一种方式（也有其他方式）替换

left join NOTES as c3 on c3.LOPRECID =c.recid

与

OUTER APPLY (SELECT TOP 1 MODIFIEDDATE, MODIFIEDBY 
             FROM NOTES AS N 
             WHERE N.LOPRECID = c.recid AND N.rectype='CS'
             ORDER BY MODIFIEDDATE DESC
) AS c3

并从WHERE子句中删除c3.rectype='CS' 。

在NOTES中没有满足rectype ='CS'要求的行的情况下，您将需要确保获得期望的结果，因为这会为您的要求在齿轮中添加一些沙子。

Answer 2

LEFT JOIN 
(
   SELECT LOPRECID, MODIFIEDDATE, MODIFIEDBY, 
     rn = ROW_NUMBER() OVER (PARTITION BY LOPRECID ORDER BY MODIFIEDDATE DESC)
   FROM dbo.Notes
) AS C3
ON C3.LOPRECID = c.recid AND C3.rn = 1