see here:

http://support.sas.com/documentation/cdl/en/lrdict/64316/HTML/default/viewer.htm#a001466799.htm

If you want to create reproducible streams of random numbers, then specify STREAMINIT before any calls to the RAND random number function. If you call the RAND function before you specify a seed with STREAMINIT (or if you specify a nonpositive seed value in the STREAMINIT function), then the RAND function uses a call to the system clock to seed itself. Each DS2 program honors one STREAMINIT seed. The prevailing seed value is the one that is specified prior to the first RAND function call. For more information, see Seed Values in SAS Functions and CALL Routines: Reference.

If you do not have this satement, then everytime you run this code you will get different dataset

http://support.sas.com/documentation/cdl/en/ds2ref/67313/HTML/default/viewer.htm#n02tlu8v5cs6efn12f5t9g5of408.htm
hope it works

多谢

没太明白！您能说的简单一些吗？多谢了