[Tex/LaTex] Double cell border for table (for an entire column)

Question

Hi what I'm trying to do is getting an "empty" column on a table.

Having an empty row is easy by adding a \hline twice. Like here:

\documentclass[12pt]{article}

\begin{document}

\begin{tabular}{|c|c|c|c|}  
\hline 
 & headline1 & headline2 & headline3 \\ 
\hline 
\hline % <-- extra one giving my an "empty" row
row1 & a & b & c \\ 
\hline 
row2 & d & e & f \\ 
\hline 
row3 & g & h & i \\ 
\hline 
\end{tabular} 

\end{document}

Is there a way of having the same on a column ? E.g. between "row1" and "a".

I tried to ad an additional | on the definition (\begin{tabular}{|c||c|c|c|}), but the horizontal lines are displayed (due to \hline causes a line on the whole width of the table)

\documentclass[12pt]{article}

\begin{document}

\begin{tabular}{|c||c|c|c|}  %<-- change here
\hline 
 & headline1 & headline2 & headline3 \\ 
\hline 
\hline 
row1 & a & b & c \\ 
\hline 
row2 & d & e & f \\ 
\hline 
row3 & g & h & i \\ 
\hline 
\end{tabular} 

\end{document}

What I want to have is this output, but without the red circled borders (I want to have it like the green one):

This is how the column should appear:

Answer 1

You can use the hhline package.

\documentclass[12pt]{article}
\usepackage{hhline}
\begin{document}
\begin{tabular}{|c||c|c|c|}  %<-- change here
  \hhline{-||---}
  & headline1 & headline2 & headline3 \\ 
  \hhline{=::===}
  row1 & a & b & c \\ 
  \hhline{-||---}
  row2 & d & e & f \\ 
  \hhline{-||---}
  row3 & g & h & i \\ 
  \hhline{-||---}
\end{tabular} 
\end{document}