Full-width tabular with column width as needed

Question

I am translating HTML-tables to latex counterparts.

In HTML, I have a table with full width that distributes the column according to their content.

So this leads to equally spaced columns,

<table style="width: 100%;">
    <tr>
        <td>a</td>
        <td>a</td>
    </tr>
</table>

whereas this assigns 4 times as much space to the left column:

<table style="width: 100%;">
    <tr>
        <td>aaaa</td>
        <td>a</td>
    </tr>
</table>

See also here for a nested example: https://jsfiddle.net/49nhmqLu/1/

tabularx

I have found that for tabularx an X column takes the remaining space:

\begin{tabularx}{\textwidth}{lX}

but there multiple X-columns would distribute the width equally, not as needed by the content. (XX would be 50:50, XXX would be 33:33:33)

My question: Is it possible to have a column type that distributes width relatively to the content? like my aaaa - a (i.e. 80:20 here) example?

Additional requirement

Actually, the content of the tabular cells may itself consist of tabularx's 🙈. So I have found that tabularx-in-tabularx seems to be impossible.

If I use outer tabulars, i can only arrive at full textwidth by having minipages inside:

If I do not insist on the content-aware column widths, I can use tabular outside and use minipages with fixed widths (eg two columns with .47\textwidth each) inside.

\begin{tabular}
\begin{minipage}[t]{0.47\columnwidth}
left outer
\end{minipage} &
\begin{minipage}[t]{0.47\columnwidth}
    \begin{tabularx}{\textwidth}{lX}
    inner left &
    inner right
    \end{tabularx}
\end{minipage}
\\
\end{tabular}

I am absolutely clueless how to get an automatic width distribution to work here, the latter example will always be 50:50.

Note that I am not insiting on an outer tabular. Anything else that distributes with according to content is fine as well. In HTML one could use e.g. <div>'s here

In the best case there would exist an environment tabularxyz which allows:

\begin{tabularxyz}
  left outer
&
  \begin{tabularx}{\textwidth}{lX}
    inner left &
    inner right
  \end{tabularx}
\\
\end{tabularxyz}

where Latex determines the optimal width for all columns, just as tabulary does this (but only for plain text contents).

The nested tabularx's are the result of a placeholder substitution from my reporting software. Most of the time, they are even just used without a surrounding table. I use tabularx because it allows to use full available textwidth.

Answer 1

tabular* will fix the tabular's width to the textwidth.

For the tabular inside a tabular cell, you could use the multirow package. You can specify cells containing multiple rows/columns (and both) with it. Examples can be found here.

Answer 2

To obtain X columns with lengths in a certain ratio, you have to use the syntax >\hsize=x_i\hsize}X, where x_i is a coefficient for the i-th X column which is proportional to the desired fraction of the total free length, and such that the sum of the coefficients is equal to the total number of X columns.

For example, to have the ratio 80/20 with two X columns, you would have to solve the (easy) linear system:

x_1/80=x_2/40, x_1+x_2=2, whence, in the table preamble:

>{\hsize=1.6\hsize}X>{\hsize=0.4\hsize}X.