Rotated Side Header Latex Table

Question

I want this my latex table to have an additional column with a rotated-side header. I tried these answers but can not make headway.

\documentclass{article}
\usepackage{booktabs, multirow}
\usepackage{graphicx, float}
\begin{document}
    \begin{table}[H]
        \centering
        \footnotesize
        \label{tabb111}
        % Please add the following required packages to your document preamble:
        % \usepackage{multirow}
        % \usepackage{graphicx}
        \resizebox{\textwidth}{6.25em}{%
            \begin{tabular}{|l|c|c|c|c|c|c|c|c|c|}
                \hline
                \multicolumn{1}{|c|}{\multirow{2}{}{}} &       \multicolumn{3}{c|}{\textbf{Min. RMSE}}           & \multicolumn{3}{c|}{\textbf{Rank}} & \multicolumn{3}{c|}{\textbf{Block Length}} \ \cline{2-10} 
                \multicolumn{1}{|c|}{} & \multicolumn{1}{l|}{$\phi = 0.8$} & \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &   \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} \ \hline
                \textbf{NBB}   & 1.57          & 0.97          & 1.43          & 5     & 5.0     & 5     & 6     & 4    & 3   \ \hline
                \textbf{MBB1}  & 1.57          & 0.9           & 1.26          & 3     & 3.5     & 4     & 2     & 2    & 4   \ \hline
                \textbf{MBB2}  & 1.57          & 0.9           & 1.26          & 3     & 3.5     & 3     & 2     & 2    & 6   \ \hline
                \textbf{MBB3}  & 1.57          & 0.89          & 1.21          & 3     & 2.0     & 2     & 2     & 9    & 6   \ \hline
                \textbf{CBB}   & \textbf{1.44} & \textbf{0.19} & \textbf{0.09} & 1     & 1.0     & 1     & 2     & 4    & 8   \ \hline
            \end{tabular}%
        }
         \resizebox{\textwidth}{6.25em}{%
            \begin{tabular}{|l|c|c|c|c|c|c|c|c|c|}
                \hline
                \multicolumn{1}{|c|}{\multirow{2}{}{.}} & \multicolumn{3}{c|}{\textbf{Value}}          & \multicolumn{3}{c|}{\textbf{Rank}} & \multicolumn{3}{c|}{\textbf{Block Length}} \ \cline{2-10} 
                \multicolumn{1}{|c|}{} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} \ \hline
                \textbf{NBB}  & 4.72          & 2.92          & 4.28         & 5       & 5.0     & 5    & 6    & 4    & 3   \ \hline
                \textbf{MBB1} & 4.71          & 2.69          & 3.78         & 3       & 3.5     & 4    & 2    & 2    & 4   \ \hline
                \textbf{MBB2} & 4.71          & 2.69          & 3.77         & 3       & 3.5     & 3    & 2    & 2    & 6   \ \hline
                \textbf{MBB3} & 4.71          & 2.67          & 3.64         & 3       & 2.0     & 2    & 2    & 9    & 6   \ \hline
                \textbf{CBB}  & \textbf{2.49} & \textbf{0.02} & \textbf{0.8} & 1       & 1.0     & 1    & 7    & 7    & 8   \ \hline
            \end{tabular}%
        }
    \end{table}
\end{document}

Just

Answer 1

With {NiceTabular} of nicematrix.

\documentclass{article}
\usepackage{nicematrix}
\begin{document}
\begin{table}[h]
\centering
\footnotesize
\begin{NiceTabular}{l>{\bfseries}lccccccccc}[hvlines]
\RowStyle{\bfseries}
\Block{*-1}{\rotate M=121}
& \Block{2-1}{} & \Block{1-3}{Min. RMSE} &&& \Block{1-3}{Rank} &&& \Block{1-3}{Block Length} \ 
& & $\phi = 0.8$ & $\phi = 0.9$ & $\phi = 0.95$ & $\phi = 0.8$ & $\phi = 0.9$ & $\phi = 0.95$ & $\phi = 0.8$ & $\phi = 0.9$& $\phi = 0.95$ \ 
& NBB   & 1.57          & 0.97          & 1.43          & 5     & 5.0     & 5     & 6     & 4    & 3   \ 
& MBB1  & 1.57          & 0.9           & 1.26          & 3     & 3.5     & 4     & 2     & 2    & 4   \ 
& MBB2  & 1.57          & 0.9           & 1.26          & 3     & 3.5     & 3     & 2     & 2    & 6   \ 
& MBB3  & 1.57          & 0.89          & 1.21          & 3     & 2.0     & 2     & 2     & 9    & 6   \ 
& CBB   & \textbf{1.44} & \textbf{0.19} & \textbf{0.09} & 1     & 1.0     & 1     & 2     & 4    & 8   \ 
\end{NiceTabular}
\end{table}
\end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).

Answer 2

Using rotatebox from graphicx package.

\documentclass{article}
\usepackage{booktabs, multirow}
\usepackage{graphicx, float}
\begin{document}
    \begin{table}[H]
        \centering
        \footnotesize
        \label{tabb111}
        % Please add the following required packages to your document preamble:
        % \usepackage{multirow}
        % \usepackage{graphicx}
        \resizebox{\textwidth}{6.25em}{%
            \begin{tabular}{|c|l|c|c|c|c|c|c|c|c|c|}
                \hline
                \multirow{7}{}{\rotatebox[origin=c]{90}{\textbf{n=121}}} &
                \multicolumn{1}{|c|}{\multirow{2}{}{}} &       \multicolumn{3}{c|}{\textbf{Min. RMSE}}           & \multicolumn{3}{c|}{\textbf{Rank}} & \multicolumn{3}{c|}{\textbf{Block Length}} \ \cline{2-11} 
                & \multicolumn{1}{|c|}{} & \multicolumn{1}{l|}{$\phi = 0.8$} & \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &   \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} \ \cline{2-11}
                & \textbf{NBB}   & 1.57          & 0.97          & 1.43          & 5     & 5.0     & 5     & 6     & 4    & 3   \ \cline{2-11}
                & \textbf{MBB1}  & 1.57          & 0.9           & 1.26          & 3     & 3.5     & 4     & 2     & 2    & 4   \ \cline{2-11}
                & \textbf{MBB2}  & 1.57          & 0.9           & 1.26          & 3     & 3.5     & 3     & 2     & 2    & 6   \ \cline{2-11}
                & \textbf{MBB3}  & 1.57          & 0.89          & 1.21          & 3     & 2.0     & 2     & 2     & 9    & 6   \ \cline{2-11}
                & \textbf{CBB}   & \textbf{1.44} & \textbf{0.19} & \textbf{0.09} & 1     & 1.0     & 1     & 2     & 4    & 8   \ \hline
            \end{tabular}%
        }
         \resizebox{\textwidth}{6.25em}{%
            \begin{tabular}{|c|l|c|c|c|c|c|c|c|c|c|}
                \hline
                \multirow{7}{}{\rotatebox[origin=c]{90}{\textbf{n=1200}}} &
                \multicolumn{1}{|c|}{\multirow{2}{}{.}} & \multicolumn{3}{c|}{\textbf{Value}}          & \multicolumn{3}{c|}{\textbf{Rank}} & \multicolumn{3}{c|}{\textbf{Block Length}} \ \cline{2-11} 
                & \multicolumn{1}{|c|}{} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} & \multicolumn{1}{l|}{$\phi = 0.8$} &    \multicolumn{1}{l|}{$\phi = 0.9$} & \multicolumn{1}{l|}{$\phi = 0.95$} \ \cline{2-11}
                & \textbf{NBB}  & 4.72          & 2.92          & 4.28         & 5       & 5.0     & 5    & 6    & 4    & 3   \ \cline{2-11}
                & \textbf{MBB1} & 4.71          & 2.69          & 3.78         & 3       & 3.5     & 4    & 2    & 2    & 4   \ \cline{2-11}
                & \textbf{MBB2} & 4.71          & 2.69          & 3.77         & 3       & 3.5     & 3    & 2    & 2    & 6   \ \cline{2-11}
                & \textbf{MBB3} & 4.71          & 2.67          & 3.64         & 3       & 2.0     & 2    & 2    & 9    & 6   \ \cline{2-11}
                & \textbf{CBB}  & \textbf{2.49} & \textbf{0.02} & \textbf{0.8} & 1       & 1.0     & 1    & 7    & 7    & 8   \ \hline
            \end{tabular}%
        }
    \end{table}
\end{document}