How to remove the small space separator in small numbers with SIunitx?

Question

Large numbers have a nice space separator which I want to keep. But these gaps are annoying in small numbers and I want to get rid of them. Here's a MWE showing my issue:

\documentclass[12pt,letterpaper,twoside]{book}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{siunitx}

\begin{document}

Blabla bla :
\begin{align}
    x &= \SI{32100000}{\m}, \\[1ex]
    y &= \SI{0.0123456}{\m}
\end{align}

\end{document}

Preview:

So is there a way to keep the spacings in large digit numbers, and remove the spacings in small digit numbers? I checked the SIunitx package documentation and didn't found a way yet.

Answer 1

You can tell siunitx to group only the integer part of numbers with group-digits=integer.

\documentclass[12pt]{article}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{siunitx}

\sisetup{group-digits=integer}

\begin{document}
Blabla bla:
\begin{align}
    x &= \SI{32100000}{\metre}, \\[1ex]
    y &= \SI{0.0123456}{\metre}
\end{align}
\end{document}

Answer 2

Try this

\documentclass[12pt,letterpaper,twoside]{book}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{siunitx}


\begin{document}

Blabla bla :
\begin{align}
    x &= \SI{32100000}{\m}, \\[1ex]
    y &= \SI[group-separator =]{0.0123456}{\m}
\end{align}

\end{document}