shewoqishuini 发表于 2010-3-6 22:56 
刚学sas,在添加一列新的变量时候,为什么“ total=a+b;”不行?而“total=sum(a,b);”却不行?
还请老手帮忙解答~谢谢~
If one of a or b is missing the total=a+b retuens missing value. But total=sum(a,b) returns missing value ONLY if both of them are missing. Both are the same if BOTH a and b are non-missings.
That is the only difference I see.