您可以将StringComparer.InvariantCultureIgnoreCase传递给GroupBy扩展方法.

You can pass StringComparer.InvariantCultureIgnoreCase to the GroupBy extension method.

var result = source.GroupBy(a => new { a.Column1, a.Column2 }, 
                StringComparer.InvariantCultureIgnoreCase);

或者您也可以按照 Hamlet Hakobyan 的建议在每个字段上使用ToUpperInvariant.我建议使用ToUpperInvariant或ToUpper而不是ToLower或ToLowerInvariant，因为它已针对程序比较进行了优化.

Or you can use ToUpperInvariant on each field as suggested by Hamlet Hakobyan on comment. I recommend ToUpperInvariant or ToUpper rather than ToLower or ToLowerInvariant because it is optimized for programmatic comparison purpose.