I have datasets for 12 countries containing a multitude of variables e.g. age, sex, tobacco use, alcohol use, diabetes, and HBP. The issue is that certain variables are missing for some countries, which means I have to clean the datasets one by one to keep the necessary variables to be finally able to append them. So I am wondering if there is and special command for appending that will only retain the variables (for each of the subsequent append) that match those on the master dataset, lets say for keeping only Age, sex and HBP.

Thanks in advance for your insights!