The short answer is it depends.
First, I suggest you read Dr. Strangedupe: Or, How I Learned to Stop Worrying And Love Duplication. There's nothing inherently bad with a duplicate question. To quote Jeff Atwood
One thing I want to be clear about, though, is that duplication is not necessarily bad. Quite the contrary — some duplication is desirable. There’s often benefit to having multiple subtle variants of a question around, as people tend to ask and search using completely different words, and the better our coverage, the better odds people can find the answer they’re looking for. And isn’t that, really, the whole point of this exercise?
The simple idea is that there are good duplicate questions. These are questions that word a concept in a slightly different why or use different keywords to describe a problem. These are actually beneficial because they are signposts to help users find duplicate questions that they might not have otherwise find.
Conversely, there are bad duplicates too. These are the duplicates that result from lack of research because googling the title or a few of the important keywords results in 5 different posts from your favorite Stack Exchange site. These questions are not sign posts because the signs already exist and we don't need another.
So if you ask a duplicate question, you need to decide for yourself. Is it a signpost to help another user avoid the same problem? If so, then leave it up. If not, delete it.