This question creates more questions. Not all compression fittings are the same. Some compression fittings are soldered on or into something, so soldering one end can unsolder the other end. Are you attempting to solder the connection with the ring and nut in place? Some compression fittings have teflon compression rings that will melt when heated. Are you going to try to stop a leak by soldering the fitting in place? – Pressure can push the liquid solder out as you try to apply it. Is the compression fitting part of an appliance? – It may have a compression fitting to permit removing the line later. Is the compression fitting joined to steel or aluminum?
I have soldered compression fittings to connect air conditioning units as they were specified for either compression or solder use. But I would just as well have removed the fitting and joined copper to copper.