An effective equation describes a weakly nonlinear wave field evolution governed by nonlinear dispersive PDEs emph{via} the set of its resonances in an arbitrary big but finite domain in the Fourier space. We consider the Schr{o}dinger equation with quadratic nonlinearity including small external random forcing/dissipation. An effective equation is deduced explicitly for each case of monomial quadratic nonlinearities $ u^2, , bar{u}u, , bar{u}^2$ and the sets of resonance clusters are studied. In particular, we demonstrate that the nonlinearity $bar{u}^2$ generates no 3-wave resonances and its effective equation is degenerate while in two other cases the sets of resonances are not empty. Possible implications for wave turbulence theory are briefly discussed.
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