When concatenating literal values with a newline separator in group_concat, always escape existing backslashes and newlines in the individual values first: replace(replace(?val, \"\\\\\\\\\" , \"\\\\\\\\\\\\\\\\\"), \"\\\\n\", \"\\\\\\\\n\"). First escape existing backslashes (\\\\ → \\\\\\\\), then escape existing newlines (newline → \\\\n). This ensures values containing these characters can be safely split on newlines later.