I have a Uno R3 and although I can add an external power supply for the SG90 micro servo it would make the project more complicated. Can I power the servo using the 5v pin of the Uno R3?
I measured the current and it does not seem to pass 160mA and in normal use, it uses only 60mA.
I'm not sure if the data sheet for every SG90 servo is the same, but if you look at this one, SG90 Specifications, you'll see the "stall current" can be between 570mA and 730mA. You may want to test your servo under this condition before deciding to power it with an Uno.
Does your servo have to push or pull anything? Or is this just to practice writing code for an unattached SG90 and see it move? If it's the former, the servo will draw more current than an Arduino can deliver so you'd need a separate power supply. If it's the latter, you can get away with it. The SG90 is about the least demanding (of current) servo available and you can drive an unloaded one directly off the Arduino. It's current-peaks should be short enough to limit thermal damage to the Arduino pin driver. Just make short test runs and don't leave it see-sawing for any length of time.
