How to do sorting with multiple column using Edge DB

Question

I'm stuck in EdgeDB query, one of my project's functionality is sort data by multiple columns. I would like to be able to specify any column, such as URL, createdDate, createdBy or any other column with different data types. Please check below code.

SELECT {
  data := (
    SELECT default::posts {
      id,
      url, 
      createdBy,
      modifiedBy,
      createdDate,
    }
    ORDER BY  (
      .url=(<optional str>$SortColumnName)??.url   
    )
  )
  )
}

I have tried this code but throwing this error

InvalidTypeError: operator '??' cannot be applied to operands of type 'std::str' and 'std::int16' Hint: Consider using an explicit type cast or a conversion function.

SELECT {
  data := (
    SELECT default::posts {
      id,
      url, 
      createdBy,
      modifiedBy,
      createdDate,
    }

    ORDER BY  (
      # .createdDate
         
      .url=(<optional str>$SortColumnName)??.url ,
      .noOfPosts=(<optional str>$SortColumnName)??.noOfPosts
      
    )
  )
}