Item 45
To create a list of unique Customer_Id values from the customer data set, which of the following techniques can be
used?
technique 1: proc SORT with NODUPKEY and OUT=
technique 2: data step with IF FIRST.Customer_Id=1
technique 3: proc SQL with the SELECT DISTINCT statement
A. only technique 1
B. techniques 1 and 2
C. techniques 1 and 3
D. techniques 1, 2, or 3


大牛们，有两个版本的答案，一个是c, 一个是d.  谁能来解解疑