\begin{table}[H]
\centering
\begin{subtable}{\textwidth}
\centering
table materials
\caption{sub table 1 }
\end{subtable}
\begin{subtable}{\textwidth}
\centering
table materials
\caption{sub table 2 }
\end{subtable}
\begin{subtable}{\textwidth}
\centering
table materials
\caption{sub table 3 }
\end{subtable}
\caption{Overall caption}
\end{table}
It always takes one whole page for a table with its subtables. So the previous page has a lot empty. So does the later page.
Thank you in advance.
subtables are necessarily wrapped in atablewhich can not break across pages. I don't know ifsubtableswork inside of alongtable, but you might explore it. Otherwise consider a restructure of your code – cmhughes Oct 24 '13 at 16:03