LaTeX Tables with merged cells & columns
\begin{tabular}{|l|l|l|l|l|l|l|}
\hline
DataSet &
\multicolumn{2}{c}{A} &
\multicolumn{2}{c}{B} &
\multicolumn{2}{c|}{C} \\
\hline
D1 & 2.1\% & 2.1\% & 2.1\% & 2.1\% & 2.1\% & 2.1\% \\
\hline
D2 & 11.6\% & 11.6\% & 11.6\% & 11.6\% & 11.6\% & 11.6\% \\
\hline
D3 & 5.5\% & 5.5\% & 5.5\% & 5.5\% & 5.5\% & 5.5\% \\
\hline
\end{tabular}\begin{array}{|c|c|}
\hline
\multicolumn{2}{|c|}{\text{Title}} \\
\hline
x & y\\ \hline
a & b\\
c & c\\
d & e\\ \hline
\end{array}\rotatebox{90.0}{ {\begin{array}{|c|c|c|}\hline
\multicolumn{2}{|c|}\rotatebox{-90.0}{ \text{ 1 } }&
\rotatebox{-90.0}{ \text{ 4 } } \\
\hline \rotatebox{-90.0}{ \text{ 5 } }&
\rotatebox{-90.0}{ \text{ 3 } } &
\rotatebox{-90.0}{ \text{ 44 } }\\
\hline \rotatebox{-90.0}{ \text{ 6 } }&
\rotatebox{-90.0}{ \text{ 4 } } &
\rotatebox{-90.0}{ \text{ 444 } }\\
\hline \end{array}} }