When I specify the width by \begin{longtable}p{xcm}
For example, here is my code
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{longtable}
\begin{document}
\newpage
\begin{longtable}{p{2cm}lp{2cm}lp{2cm}l}
\caption{Test}\\
\label{table:sh}\\
\hline\hline
2cm & 2cm & 2cm \\
\hline
Test & test & test \\
\end{longtable}
\begin{longtable}{p{4cm}lp{4cm}lp{4cm}l}
\caption{Test}\\
\label{table:sh}\\
\hline\hline
4cm & 4cm & 4cm \\
\hline
Test & test & test \\
\end{longtable}
\end{document}
And clearly the first and third column width have been changed but not the middle column. Why is that? How to fix it?