答案1
我认为你的意思是这样的:
\documentclass{scrbook}
\usepackage{tabularx}
\usepackage{booktabs}
\begin{document}
\begin{tabularx}{\textwidth}{XXXXXXXX}
\multicolumn{4}{l}{Title 1} & \multicolumn{4}{l}{Title 2} \\
\cmidrule(lr){1-4} \cmidrule(lr){5-8}
Sub1&Sub2&Sub3&Sub4&Sub1&Sub2&Sub3&Sub4 \\
\midrule
A & B & C & D & A & B & C & D \\
A & B & C & D & A & B & C & D \\
A & B & C & D & A & B & C & D \\
A & B & C & D & A & B & C & D \\
A & B & C & D & A & B & C & D \\
A & B & C & D & A & B & C & D \\
\midrule
\end{tabularx}
\end{document}