SELECT TOP 1000 [chClientCode] ,[nvcClientName] ,[chRegionCode] ,isnull(chUltimateHeadClientCode,[chClientCode]) as chUltimateHeadClientCode FROM [PwCMDM_V1].[Core].[tblClient]
Define:
isnull(expression,replacement_value)
SQL判断如果一列值为null则取另一列值代替 isnull()
原文：http://www.cnblogs.com/dangkei/p/4119052.html