如何在SQL Server中将可空值更改为非空值？

Question

我使用union查询合并了三个表，并为所有列创建了group by function。

这是我的代码：

S1

这里我设置select Id, Firstname, Mark1, Mark2, Mark3 from (select Id, Firstname, Null as Mark1, Null as Mark2, Null as Mark3 from Parent union select Id, Null as Firstname, Mark1, Mark2, Null as Mark3 from Child union select Id, Null as Firstname, Null as Mark1, Null as Mark2, Mark3 from Mark) t where Mark3 is not null group by Id, Firstname, Mark1, Mark2, Mark3 不是null使用where条件所以我的问题是如何使用where condition将null值更改为非null为其余字段？

Answer 1

从您的查询中我建议使用join而不是（与null值结合） 所以试试这个

Select parent.Id , parent. firstName, child.mark1,child.mark2,mark.mark3
From parent 
inner join child on parent.id =child.id
Inner join mark on mark.id=parent.id