edit: do you mean net salary?
45k/year is enough for a single person or even a couple living more frugal.
If single, you will have a blast in Berlin with 45k. If you're moving with a dependent, that's a bit tight (as a newcomer, you will never find the best deals regarding accommodation, there's a fair supply of newly built apartments in Berlin, but they aren't cheap).
[1] https://www.numbeo.com/cost-of-living/compare_cities.jsp?cou...
For information in Paris, currently I'm at ~50K a year "Brut", which means ~35K a year "Net" ("go home" salary).
I'm costing ~75K per year to my employer in term of salary (there are taxes on his side to).
My rent, for a small flat (22 square meters) in Paris is around 10K per year.
My taxes are around 6K per year.
I'm an SRE/software engineer with ~8 years experience.
Ladies and gentlemen of the world, this is what is costs to have our (indeed very nice) social security/health insurance !