Of course we are talking about asana here not Yoga. So I'll answer that question.
Students who are used to a certain level of physical exercise, who train regularly, who support that training with proper rest and nutrition, those students can do both practices on the same day with little to no issues.
Those who are not in this sort of conditioning can (and do) still do both on the same day however they often lose the integrity of an alignment-based practice when they are on their own (read: without a sound teacher) or when they are fatigued (knowingly or unknowingly). Of course those folks still DO it but it often comes with heightened risk and reduced effect.
So you'll have to determine which of the above fits you.
As for the order of the doing, I have found that the practice of asana is more helpful when it follows a workout rather than preceding it. My view would change, albeit slightly, if there were something following a workout that replicated the effects of Savasana (moving the central nervous system into a parasympathetic state). Once the nerves are calmed thus, then it's best not to jar or rattle them, at least for a while:-)
Hope this is helpful to your path.