We discuss neutrino production in accretion flows onto supermassive black holes. First, we consider accretion flows in active galactic nuclei (AGN). Luminous and low-luminosity AGN have hot coronae and radiatively inefficient accretion flows (RIAFs), respectively, where cosmic-ray protons can be accelerated by stochastic turbulence acceleration. These cosmic rays produce TeV - PeV neutrinos via interaction with ambient matter and photons. Our scenario can explain cosmic TeV--PeV neutrino and keV--MeV photon backgrounds without contradicting cosmic GeV--TeV photon background. Future neutrino observations will provide a solid test to our scenario. We also apply this scenario to tidal disruption events (TDEs), and our hot corona model could be consistent with the neutrino events reported as the associations with nearby TDEs. To test TDE-neutrino association, deep and wide optical follow-up observations are important, which can be done by near-future optical astronomical facilities.