mybaits does not support the "variant" data type.

Due to the company's project, sql server is used, and then there is a data type that does not support "variant";
variant: it can store many formats. For example, a sql_variant column can store both numbers and text.

Of course, because of this feature, they must undergo some conversions when reading, otherwise they don't know what type.

So just cast(a.name as varchar(100)) just works