Dear all
From the entire sample list ,I would like to create a sub-sample based on certain condtions.Say, I have 3 variables,assets,profits&sales.I want to create a subsample by imposing certain conditions on the specified variables and here is what I did.

gen estsample = 1 if assets>=0&profits>100&sales<200000.
It turns out that wherever the values are missing for all of these, estample 1 is created. I want stata to keep it as missing ,if either of these variables are missing.How to do this
Thanks in advance