  We prove weak-strong uniqueness results for the compressible Navier-Stokes
system with degenerate viscosity coefficient and with vacuum in one dimension.
In other words, we give conditions on the weak solution constructed in
\cite{Jiu} so that it is unique. The novelty consists in dealing with initial
density $\rho_0$ which contains vacuum. To do this we use the notion of
relative entropy developed recently by Germain, Feireisl et al and Mellet and
Vasseur (see \cite{PG,Fei,15}) combined with a new formulation of the
compressible system (\cite{cras,CPAM,CPAM1,para}) (more precisely we introduce
a new effective velocity which makes the system parabolic on the density and
hyperbolic on this velocity).
