\begin{table}
\centering
\begin{tblr}[         %% tabularray outer open
]                     %% tabularray outer close
{                     %% tabularray inner open
colspec={Q[]Q[]},
}                     %% tabularray inner close
\toprule
a & b \\ \midrule %% TinyTableHeader
- &  3 \\
1 & - \\
2 &  5 \\
\bottomrule
\end{tblr}
\end{table} 
