\begin{equation} \label{eq_a}
x=
\left\{
\begin{aligned}
a &, & & x=0 \\
b &, & & x=1 \\
c &, & & x=2
\end{aligned}
\right.
\end{equation}

\begin{equation} \label{eq_b}
x=
\left\{
\begin{array}{c c}
a &, & & x=0 \\
b &, & & x=1 \\
c &, & & x=2
\end{array}
\right.
\end{equation}