在我看来，下面的指令产生了一些额外的空间。
\documentclass[12pt,a4paper,russian]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[russian]{babel}
\usepackage{datatool,xspace,cleveref}
\newcommand{\createGostDb}[1]{%
% param-1: DB
\DTLgnewdb{#1}
\DTLaddcolumn{#1}{number}
\DTLaddcolumn{#1}{app}
}
\newcommand{\loadGostDb}[1]{\DTLloaddb{db}{#1}}
% https://tex.stackexchange.com/questions/498022/update-values-in-datatool
\newcommand*\dtlupdaterefsincurrentrow{\dtlupdateentryincurrentrow{app}}
\newcommand\appender[3]{%
% param-1: DB
% param-2: gostId
% param-3: appendable section ref
\DTLgetvalueforkey{\oldSecRefs}{app}{#1}{number}{#2}%
\edtlgetrowforvalue{#1}{\dtlcolumnindex{#1}{number}}{#2}%
\expandafter\dtlupdaterefsincurrentrow\expandafter{\oldSecRefs, \Cref{#3}}%
\dtlrecombine%
}
\newcommand{\addGost}[3]{
% param-1: datatool DB
% param-2: gostId
% param-3: reference
\DTLnewrow{#1}%
\DTLnewdbentry{#1}{number}{#2}
\DTLnewdbentry{#1}{app}{\Cref{#3}}
}
\newcommand{\getGostNumberById}[1]{%
\DTLgetvalueforkey{\name}{number}{db}{gostID}{#1}\name\xspace%
}
\newcommand{\getGostYearById}[1]{%
\DTLgetvalueforkey{\year}{year}{db}{gostID}{#1}\year\xspace%
}
\newcommand{\getGostTitleById}[1]{%
\DTLgetvalueforkey{\title}{title}{db}{gostID}{#1}\title\xspace%
}
\newcommand{\emplaceGost}[2]{%
% param-1: gostId
% param-2: which section appear
\getGostNumberById{#1}\xspace%
\dtlgetrowindex{\currentrowidx}{gost}{\dtlcolumnindex{gost}{number}}{#1}%
\ifx\currentrowidx\dtlnovalue
% Not Found
\addGost{gost}{#1}{#2}%
\else
% Found in row \currentrowidx.
\appender{gost}{#1}{#2}%
\fi
}
\begin{document}
\loadGostDb{db.csv}
\createGostDb{gost}
\Crefname{section}{}{}
\Crefname{appendix}{App.}{Apps.}
\section{Some section}
\subsection{Some subsection}\label{i}
Why this command produces the extra spaces between the quotes <<\emplaceGost{GOST1552}{i}>>?
\subsection{Another subsection}\label{ii}
The same effect you can find here <<\getGostNumberById{GOST1552}>>\ldots
\appendix
\section{Show}\label[appendix]{ii}
<<\emplaceGost{GOST1553}{ii}>>,
<<\emplaceGost{GOST1552}{ii}>>.
\end{document}
db.csv内容：
\begin{filecontents*}{db.csv}
gostID,number,title,year
GOST1552,ГОСТ 1552,Об этом ГОСТ, 98
GOST1553,ГОСТ 1553,О том ГОСТ, 99
\end{filecontents*}
答案1
如果我删除 \xspace 并且还抑制各种虚假空格，%空格就会消失：
\documentclass[12pt,a4paper,russian]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[russian]{babel}
\usepackage{datatool,xspace,cleveref}
\newcommand{\createGostDb}[1]{%
% param-1: DB
\DTLgnewdb{#1}%
\DTLaddcolumn{#1}{number}%
\DTLaddcolumn{#1}{app}%
}
\newcommand{\loadGostDb}[1]{\DTLloaddb{db}{#1}}
% https://tex.stackexchange.com/questions/498022/update-values-in-datatool
\newcommand*\dtlupdaterefsincurrentrow{\dtlupdateentryincurrentrow{app}}
\newcommand\appender[3]{%
% param-1: DB
% param-2: gostId
% param-3: appendable section ref
\DTLgetvalueforkey{\oldSecRefs}{app}{#1}{number}{#2}%
\edtlgetrowforvalue{#1}{\dtlcolumnindex{#1}{number}}{#2}%
\expandafter\dtlupdaterefsincurrentrow\expandafter{\oldSecRefs, \Cref{#3}}%
\dtlrecombine%
}
\newcommand{\addGost}[3]{%
% param-1: datatool DB
% param-2: gostId
% param-3: reference
\DTLnewrow{#1}%
\DTLnewdbentry{#1}{number}{#2}%
\DTLnewdbentry{#1}{app}{\Cref{#3}}%
}
\newcommand{\getGostNumberById}[1]{%
\DTLgetvalueforkey{\name}{number}{db}{gostID}{#1}\name%
}
\newcommand{\getGostYearById}[1]{%
\DTLgetvalueforkey{\year}{year}{db}{gostID}{#1}\year%
}
\newcommand{\getGostTitleById}[1]{%
\DTLgetvalueforkey{\title}{title}{db}{gostID}{#1}\title%
}
\newcommand{\emplaceGost}[2]{%
% param-1: gostId
% param-2: which section appear
\getGostNumberById{#1}%
\dtlgetrowindex{\currentrowidx}{gost}{\dtlcolumnindex{gost}{number}}{#1}%
\ifx\currentrowidx\dtlnovalue
% Not Found
\addGost{gost}{#1}{#2}%
\else
% Found in row \currentrowidx.
\appender{gost}{#1}{#2}%
\fi
}
\begin{document}
\loadGostDb{db.csv}
\createGostDb{gost}
\Crefname{section}{}{}
\Crefname{appendix}{App.}{Apps.}
\section{Some section}
\subsection{Some subsection}\label{i}
Why this command produces the extra spaces between the quotes <<\emplaceGost{GOST1552}{i}>>?
\subsection{Another subsection}\label{ii}
The same effect you can find here <<\getGostNumberById{GOST1552}>>\ldots
\appendix
\section{Show}\label[appendix]{ii}
<<\emplaceGost{GOST1553}{ii}>>,
<<\emplaceGost{GOST1552}{ii}>>.
\end{document}
