  We study 1D NLS with non-gauge invariant quadratic nonlinearity on the torus.
The Cauchy problem admits trivial global solutions which are constant with
respect to space. The non-existence of global solutions also has been studied
only by focusing on the behavior of the Fourier $0$ mode of solutions. However,
the earlier works are not sufficient to obtain the precise criteria for the
global existence for the Cauchy problem. In this paper, the exact criteria for
the global existence of $L^2$ solutions is shown by studying the interaction
between the Fourier $0$ mode and oscillation of solutions. Namely, $L^2$
solutions are shown a priori not to exist globally if they are different from
the trivial ones.
