Are JOIN queries faster than several queries? (You run your main query, and then you run many other SELECTs based on the results from your main query)
I'm asking because JOINing them would complicate A LOT the design of my application
If they are faster, can anyone approximate very roughly by how much? If it's 1.5x I don't care, but if it's 10x I guess I do.
This is way too vague to give you an answer relevant to your specific case. It depends on a lot of things. Jeff Atwood (founder of this site) actually wrote about this. For the most part, though, if you have the right indexes and you properly do your JOINs it is usually going to be faster to do 1 trip than several.