请看问题补充的SQL code!当Months为NULL时，Months已经等于3了，为什么在DATEADD里计算的Months还是为NULL

显示全部楼层 · 2011-3-2 13:42:27

SELECT
DeptName, JoinDate,ProbationMonths, ISNULL(Months, 3) AS Months,DATEADD(month, Months, JoinDate) AS ProbationEndDate
FROM
Employee
如果我把AS Months 改为AS MM，然后DAREADD里的Months也改为MM，刚运行提示：列名‘MM‘无效。

千问 · 2011-3-2 13:42:27

AS MM 后的MM 在 DATEADD函数里不不认的，解决方法有两个1。在DATEADD中继续使用你前面用的ISNULL函数,如下SELECT
DeptName, JoinDate,ProbationMonths, ISNULL(Months, 3) AS Months,DATEADD(month, ISNULL(Months, 3), JoinDate) AS ProbationEndDateFROM
Employee2。嵌套一层SELECT emp *,DATEADD(month, Months, JoinDate) AS ProbationEndDate FROM(SELECT