linq到实体框架的问题

Question

(from dtContract in dataEntity.contracts
   where
       (
           dtContract.Supplier_ID == suppID &&
           dtContract.Contract_Year != null
       )
   orderby dtContract.Contract_Year
   select new
       {
           year = (int) dtContract.Contract_Year
       }).ToList();

上面的LINQ查询转换为以下SQL查询

SELECT 
    `Project1`.`Supplier_ID`, `Project1`.`C1`
FROM
    `contracts` AS `Project1`
WHERE
    (`Project1`.`Supplier_ID` = @p__linq__0)
        AND (`Project1`.`Contract_Year` IS NOT NULL)
ORDER BY `Project1`.`Contract_Year` ASC;

哪个是抛出异常

  

未知栏C1

请您说明这背后的原因..？