I try to answer your question, first of all, cast function belongs to SQL function, which convert an expression from one data type to another, not SAS function, so it could not be used in SAS,  Both SQL and SAS have month function, normally we use month function as month(date), result will be month, for example, month('05Mar2012'd) will get 3, both in SAS and SQL. In SQL, month(0) will get 1, so I guess month(4) will get 5, however I am not familiar with SQL, I could not give you correct answer. Could you give me some forum money? Thank you.   

好难的code.

我们经常用的netezza SQL里面没有这种month  function, 而是用这个

date_part('month' , a.saledate) as month.

能不能发更完整的code。没有上下文，很难理解吧

the complete SQL code could be like the followings, but the problem is the SAS does not have a function called cast() yet, even in SAS v9.3, so it still can't make LZ's idea work, so what does the "cast((date1+2 - date2 month(4) as int)" mean? the word 'cast' means convert and it can convert int2char or char2int or something similar! and also month('03Apr2001'd)=4, but month(4)=1, even month(0)=1 in SAS, so cast((date1+2 - date2 month(4) as int) is not valid statement for proc SQL in SAS.