  The empirical differential metallicity distribution (EDMD) is deduced for (i)
local thick disk stars; (ii) likely metal-weak thick disk stars; (iii)
chemically selected local G dwarfs, with the corrections performed in order to
take into account the stellar scale height; in addition to previous results
related to (iv) solar neighbourhood halo subdwarfs; and (v) K-giant bulge
stars. The thick disk is conceived as made of two distinct regions: the
halo-like and the bulge-like thick disk, and the related EDMD is deduced. Under
the assumption that each distribution is typical for the corresponding
subsystem, the EDMD of the thick disk, the thick + thin disk, and the Galaxy,
is determined by weighting the mass. Models of chemical evolution are computed
for each subsystem assuming the instantaneous recycling approximation. The EDMD
data are reasonably fitted by simple models implying both homogeneous and
inhomogeneous star formation, provided that star formation is inhibited during
thick disk evolution. The initial mass function (IMF) is assumed to be a
universal power law, which implies an unchanged true yield in different
subsystems. The theoretical differential metallicity distribution (TDMD) is
first determined for the halo-like thich disk, the bulge-like thick disk, and
the thin disk separately, and then for the Galaxy by weighting the mass. An
indicative comparison is performed between the EDMD deduced for the disk both
in presence and in absence of [O/Fe] plateau, and its counterpart computed for
(vi) nearby stars for which the oxygen abundance has been determined both in
presence and in absence of the local thermodynamical equilibrium (LTE)
approximation. Both distributions are found to exhibit a similar trend, though
systematic differences exist.
