siunitx table leading zeros

Question

How to preserve the leading zeros of the errors in a table using siunitx' S-column type?

\documentclass[ngerman,english]{scrreprt}

\usepackage{babel}    
\usepackage[locale=DE]{siunitx}    
\sisetup{separate-uncertainty}
\sisetup{multi-part-units=single}

\usepackage{booktabs}

\begin{document}

\selectlanguage{ngerman}    

\begin{tabular}{l*{2}{S[table-figures-decimal=1,
                        table-text-alignment=left,
                        table-number-alignment=left,
                        table-figures-uncertainty=1]}}
   \toprule
   A & {Column1 symbol $\Delta$} & {Column2 symbol $\delta$} \\
     & {Column1} & {Column2} \\
   \midrule
   B &  -5.0 \pm 1.0 & -10.0 \pm 02.0 \\
   C &   0.0 \pm 1.0 &   5.0 \pm 02.0 \\
   D & -20.0 \pm 1.0 & -100.0 \pm 20.0 \\
\bottomrule
\end{tabular}
\end{document}

Answer 1

The code in siunitx is broadly based around the idea that numbers will be normalised to a 'standard' form before printing. One of the normalisation rules is that leading zeros are removed. While there is some possibility to pad the integer part back out again, that's not the same as retaining 'excess' information in the input. As such, your best bet is to turn off the parser, as suggested in a comment:

\documentclass[
  ngerman,
  english
]{scrreprt}

\usepackage{babel}    
\usepackage{siunitx}    
\sisetup{
  locale = DE,
  separate-uncertainty,
  multi-part-units = single
}
\usepackage{booktabs}

\begin{document}

\selectlanguage{ngerman}    
\begin{table}
  \sisetup{parse-numbers = false}
  \begin{tabular}{
    l
    S[table-format = -2.1]
    @{${}\pm{}$}
    S[table-format =  1.1,table-number-alignment = left]
    S[table-format = -3.1]
    @{${}\pm{}$}
    S[table-format =  2.1,table-number-alignment = left]
  }
     \toprule
     A & \multicolumn{2}{l}{Column1 symbol $\Delta$}
       & \multicolumn{2}{l}{Column2 symbol $\delta$} \\
       & \multicolumn{2}{l}{Column1}
       & \multicolumn{2}{l}{Column2} \\
     \midrule
     B &  -5.0 & 1.0 &  -10.0 & 02.0 \\
     C &   0.0 & 1.0 &    5.0 & 02.0 \\
     D & -20.0 & 1.0 & -100.0 & 20.0 \\
    \bottomrule
  \end{tabular}
\end{table}
\end{document}