We discuss a quantum extension of the holographic RG flow equation obtained previously from the classical Hamiltonian constraint in the bulk AdS supergravity. The Wheeler-DeWitt equation is proposed to generate the extended RG flow and to produce 1/N subleading corrections systematically. Our formulation in five dimensions is applied to the derivation of the Weyl anomaly of boundary N=4 SU(N) super-Yang-Mills theory beyond the large N limit. It is shown that subleading 1/N^2 corrections arising from fields in AdS_5 supergravity agree with those obtained recently by Mansfield et al. using their Schroedinger equation, thereby guaranteeing to reproduce the exact form of the boundary Weyl anomaly after summing up all of the KK modes.

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