Table columns width are not equal

Question

Following is the code for this table:

\documentclass{article}
\usepackage{array, multirow}

\begin{document}
\begin{table}
    \centering
    \begin{tabular}{|c|*{20}{w{c}{0.5cm}|}}
        \hline
        \multirow{2}*{A} & \multicolumn{2}{c|}{1} & \multicolumn{2}{c|}{2} & \multicolumn{2}{c|}{3} & \multicolumn{2}{c|}{4} & \multicolumn{2}{c|}{5} & \multicolumn{2}{c|}{6} & \multicolumn{2}{c|}{7} & \multicolumn{2}{c|}{8} & \multicolumn{2}{c|}{9} & \multicolumn{2}{c|}{10} \\
        \cline{2-21}
        ~ & \multicolumn{2}{c|}{0} & \multicolumn{2}{c|}{0.1} & \multicolumn{2}{c|}{0.2} & \multicolumn{2}{c|}{0.3} & \multicolumn{2}{c|}{0.4} & \multicolumn{2}{c|}{0.5} & \multicolumn{2}{c|}{0.6} & \multicolumn{2}{c|}{0.7} & \multicolumn{2}{c|}{0.8} & \multicolumn{2}{c|}{0.9} \\
        \hline
        \multirow{2}*{B} & \multicolumn{5}{c|}{1} & \multicolumn{5}{c|}{2} & \multicolumn{5}{c|}{3} & \multicolumn{5}{c|}{4} \\
        \cline{2-21}
        ~ & \multicolumn{5}{c|}{1} & \multicolumn{5}{c|}{2} & \multicolumn{5}{c|}{3} & \multicolumn{5}{c|}{4} \\
        \hline
        \multirow{2}*{C} & \multicolumn{5}{c|}{1} & \multicolumn{5}{c|}{2} & \multicolumn{5}{c|}{3} & \multicolumn{5}{c|}{4} \\
        \cline{2-21}
        ~ & \multicolumn{5}{c|}{1} & \multicolumn{5}{c|}{2} & \multicolumn{5}{c|}{3} & \multicolumn{5}{c|}{4} \\        
        \hline
    \end{tabular}
    \caption{Caption}
    \label{tab:my_label}
\end{table}
\end{document}

I want for A row, the columns from 1 to 10 are equal; For B and C rows, the columns from 1 to 4 are equal.

Thanks!

--------------------------------Update---------------------------------------

The pic showed below is the table that I want.

Thanks.

Answer 1

Welcome to TeX.SE! Please, always provide MWE (Minimal Working Example), a small complete document, which reproduce your problem.

Your table has many errors:

• the most of \multicolumn ar superfluous, consequently all this overwrite column settings

• your table has only 11 columns, why you define 21?

• correct code for your table is:

\documentclass{article}
\usepackage{array, multirow}

\begin{document}
\begin{table}
    \centering
    \begin{tabular}{|c|*{10}{w{c}{0.5cm}|}}
        \hline
\multirow{2}*{A} 
    & 1 & 2   & 3   & 4   & 5   & 6   & 7   & 8   & 9   & 10 \\
        \cline{2-11}
    & 0 & 0.1 & 0.2 & 0.3 & 0.4 & 0.5 & 0.6 & 0.7 & 0.8 & 0.9 \\
        \hline
\multirow{2}*{B} 
    & 1 & \multicolumn{4}{c|}{2} 
                & 3 & \multicolumn{4}{c|}{4}        \\
    \cline{2-11}
    & 1 & \multicolumn{4}{c|}{2}
                & 3 & \multicolumn{4}{c|}{4}        \\
    \hline
\multirow{2}*{C} 
    & 1 & \multicolumn{4}{c|}{2}
                & 3 & \multicolumn{4}{c|}{4}        \\
    \cline{2-11}
    & 1 & \multicolumn{4}{c|}{2}
                & 3 & \multicolumn{4}{c|}{4}        \\
    \hline
    \end{tabular}
    \caption{Caption}
    \label{tab:my_label}
\end{table}
\end{document}

Addendum:

According to your comment and showed new desired result in edited question:

• it seems that this table formatting is not possible to get correctly with tabular, if \multicolumn cells merged more than four columns.
• as solution, I found that this can be done by use of the tabularray package:

\documentclass{article}
\usepackage{geometry}
\usepackage{tabularray}
\NewTableCommand\mcc[1]{\SetCell[c=#1]{c} }
%---------------- Show page layout. Don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%

\begin{document}
    \begin{table}[ht]
    \centering
\begin{tblr}{hlines, vlines,
             colsep=4pt,
             colspec = {*{21}{Q[c, wd=1em]} }
                 }
\SetCell[r=2]{c}    A
    & \mcc{2} 0     &   & \mcc{2} 0.1   &   & \mcc{2} 0.2   &   & \mcc{2} 0.3   &   & \mcc{2} 0.4
                    &   & \mcc{2} 0.5   &   & \mcc{2} 0.6   &   & \mcc{2} 0.7   &   & \mcc{2} 0.8 
                    &   & \mcc{2} 0.9   \\
    & \mcc{2} 1     &   & \mcc{2}   2   &   & \mcc{2}   3   &   & \mcc{2}   4   &   & \mcc{2}   5
                    &   & \mcc{2}   6   &   & \mcc{2}   7   &   & \mcc{2}   8   &   & \mcc{2}   9
                    &   & \mcc{2}   10  \\
\SetCell[r=2]{c}    B
   & \SetCell[c=5]{c} 1 &   &   &   &   
                    & \mcc{5}{2}    &   &   &   &   
                            & \mcc{5}{3}    &   &   &   &  
                                    & \mcc{5}{4}    &   &   &   &       \\
   & \SetCell[c=5]{c} 1 &   &   &   &
                    & \mcc{5}{2}    &   &   &   &
                            & \mcc{5}{3}    &   &   &   &
                                    & \mcc{5}{4}    &   &   &   &       \\
\SetCell[r=2]{c}    C
   & \SetCell[c=5]{c} 1 &   &   &   &
                    & \mcc{5}{2}    &   &   &   &
                            & \mcc{5}{3}    &   &   &   &
                                    & \mcc{5}{4}    &   &   &   &       \\
   & \SetCell[c=5]{c} 1 &   &   &   &
                    & \mcc{5}{2}    &   &   &   &
                            & \mcc{5}{3}    &   &   &   &
                                    & \mcc{5}{4}    &   &   &   &       \\
\end{tblr}
\caption{Caption}
\label{tab:my_label}
    \end{table}
\end{document}

(red lines indicate page layout)