案例声明为ISNULL

Question

我对T-SQL还是很陌生，并希望使用isull简化此查询。

case 
when datediff(d, appdate, disdate) IS NOT NULL THEN datediff(d, appdate, disdate) 
ELSE 
    Case 
        when appdate is null THEN datediff(d,update,getdate())
        when disdate IS NULL THEN datediff(d,appdate,getdate())
    END
END

Answer 1

没有太多简化，但这应该做同样的事情：

ISNULL(datediff(d, appdate, disdate) , 
    CASE WHEN appdate IS NULL THEN datediff(d,update,getdate())
         WHEN disdate IS NULL THEN datediff(d,appdate,getdate()) END
)