Sql 林克没有'；“我不能和一个”一起工作；选择isnull"；查询

可能重复：

我在LINQ中尝试了以下查询：

   string query = @"SELECT ISNULL(P.firstname, s.firstname) AS Expr1,ISNULL(P.lastname,
  s.lastname) AS Expr2 FROM comment AS C LEFT OUTER JOIN professor AS P ON P.ID =   

  C.PID LEFT OUTER JOIN student AS s ON s.ID = C.SID

  WHERE (C.VID = 2)";

        ArrayList allNames=null;
        using (var context = new NewsReaderEntities())
        {
            ObjectQuery<string> results = context.CreateQuery<string>(query);
         //   ObjectQuery<string> results1 = context.CreateQuery<string>
             (query1,parameters);
            foreach (string result in results )
            {
                allNames.Add(result);

            }
        }

        return allNames;



    }

这也会引起一个错误

两者在SQL管理中都可以正常工作。有什么想法吗？

参见以下示例：

var query = from p in Pets select p;
if (OwnerID != null) query = query.Where(x => x.OwnerID == OwnerID);
if (AnotherID != null) query = query.Where(x => x.AnotherID == AnotherID);
if (TypeID != null) query = query.Where(x => x.TypeID == TypeID);

---

希望这对您有所帮助

您是否尝试过谷歌搜索“linq isnull”-它会返回这个问题，我相信这会回答您的问题-

var query = from p in Pets select p;
if (OwnerID != null) query = query.Where(x => x.OwnerID == OwnerID);
if (AnotherID != null) query = query.Where(x => x.AnotherID == AnotherID);
if (TypeID != null) query = query.Where(x => x.TypeID == TypeID);