code: func (col *Column) String() string {
  	result := col.ColName.L
  	if col.TblName.L != "" {
  		result = col.TblName.L + "." + result
  	}
  	if col.DBName.L != "" {
  		result = col.DBName.L + "." + result
  	}
  	return result
  }
docs: // String implements Stringer interface.