code: func NewDecimalFieldDescriptor(nullable NullableColumn) FieldDescriptor {
  	return &decimalFieldDescriptor{
  		baseFieldDescriptor: baseFieldDescriptor{
  			fieldType:  mysql_proto.FieldType_DECIMAL,
  			isNullable: nullable,
  		},
  	}
  }
docs: // This returns a field descriptor for FieldType_DECIMAL (i.e., Field_decimal)