Question about Sales Forecast Using PROC MIXED

[akilees]

I'm new to SAS and studying a forecasting problem for the sales of a kind of soft drink.  I have about 20 variables(including week, price,  competitors price/volume, promotion dummy, holiday/season dummy) and 100 weeks data.

I used stepwise/forward/backward to select some variables first.  It turns out the best model is forward and I got about 10 variables from it.  Then I tried to do the pooled regression using proc mixed but I don't know what to put in random statement what to put in sub= etc.  I searched a lot and most examples only have two or three variables.  I got so confused, anyone can help me?

Thanks!!