SQL : Split one row into two rows depending on column

Question

如果这是重复的，我很抱歉。请指出我正确的问题。我使用的是 SQL SERVER 2008。我使用下面的查询，因为我需要从 3 个表中获取数据。

SELECT qc.FileID as [FileID],    
qc.QID1 as [QID1],    
xqs.SID1 as [SID1],   
xqc.CID1 as [CID1],  
xqs.Comments as [SComments],  
xqc.Comments as [CComments]  
FROM QCTable(nolock) qc  
JOIN QCSectionTable (nolock) xqs ON qc.QCID = xqs.QCID  
LEFT JOIN QCChargeTable (nolock) xqc ON xqc.QCXrefID = xqs.QCXrefID

对于上面我得到这个
FieID1 SID1 SID1 CID1 SComments CComments

我有一排像下面

FileID1  QID1 SID1 CID1 SComments  CComments

我需要将上面的行拆分为

FileID1 QID1 SID1 null SComments
FileID1 QID1 SID1 CID1 CComments

提前致谢。

Answer 1

最简单的方法是union all :

select FileID1, QID1, SID1, null as cId1, SComments
from table t
union all
select  FileID1, QID1, SID1, cId1, CComments
from table t;

如果您有大量数据，使用 cross apply 执行此操作会更快一些或 cross join :

select v.*
from table t cross apply
     (values (FileID1, QID1, SID1, null, SComments),
             (FileID1, QID1, SID1, cId1, CComments)
     ) v(FileID1, QID1, SID1, cId1, CComments);

优点是这只会扫描表一次。