C# 在C/ASP.NET中，对列求和会导致null

我使用以下sql语句计算列的和：

 select coalesce(SUM(cdin_ActMortgageAmnt),0) 
 from CDIndex,company  
 where  comp_companyid=cdin_companyid and comp_idcust like '%10319%' 
 and cdin_Deleted is null and cdin_startunstufdate is not null 
 and cdin_Status='InProgress'

给我这样的输出：

var sumation = (from com in db.Companies
                join cd in db.CDIndexes on com.Comp_CompanyId equals cd.cdin_CompanyId
                where
                    cd.cdin_Status == "InProgress" &&
                    cd.cdin_startunstufdate == null &&
                    cd.cdin_Deleted == null
                select new {
                    sum = cd.cdin_ActMortgageAmnt 
                }
               );

var summ = sumation.Sum(x => x.sum);

var summ = db.Companies.Join(
    db.CDIndexes,
    cd => cd.cdin_CompanyId,
    com => Comp_CompanyId,
    (com, cd) => new { com, cd })
  .Where(z=>z.com.comp_idcust.Contains("10319") // Added "LIKE"
    && z.cd.cdin_Status == "InProgress" 
    && z.cd.cdin_startunstufdate != null // Reversed your condition
    && z.cd.cdin_Deleted == null)
  .Sum(z=>z.cd.cdin_ActMortgageAmnt);

我尝试将其转换为LINQ，如下所示：

var sumation = (from com in db.Companies
                join cd in db.CDIndexes on com.Comp_CompanyId equals cd.cdin_CompanyId
                where
                    cd.cdin_Status == "InProgress" &&
                    cd.cdin_startunstufdate == null &&
                    cd.cdin_Deleted == null
                select new {
                    sum = cd.cdin_ActMortgageAmnt 
                }
               );

var summ = sumation.Sum(x => x.sum);

var summ = db.Companies.Join(
    db.CDIndexes,
    cd => cd.cdin_CompanyId,
    com => Comp_CompanyId,
    (com, cd) => new { com, cd })
  .Where(z=>z.com.comp_idcust.Contains("10319") // Added "LIKE"
    && z.cd.cdin_Status == "InProgress" 
    && z.cd.cdin_startunstufdate != null // Reversed your condition
    && z.cd.cdin_Deleted == null)
  .Sum(z=>z.cd.cdin_ActMortgageAmnt);

在调试模式下，当我将跟踪点放在var summ旁边时，当我指向它时，它会给我null

---

问题是什么？

在您的案例中，您使用的是coalesceSUMcdin\u ActMortgageAmnt，0，因为cdin\u ActMortgageAmnt的某些值可以为空，并且您将默认值设置为0，因此您需要在最终查询中执行相同的操作。当您执行选择时，会出现类似这样的情况

cd.cdin_ActMortgageAmnt ?? 0

---

此查询适合您的sql查询

     var sumation =db.Companies.Join(db.CDIndexes,
                                        com=>com.Comp_CompanyId,
                                        cd=>cd.cdin_companyid,
                                        (com,cd)=>new {com,cd})
                                   .Where(x=>x.com.comp_idcust.Contains("10319") && x.cd.cdin_Status== "InProgress" &&
                                          cd.cdin_startunstufdate != null &&
                                          cd.cdin_Deleted == null)
                                   .Select(x=>new 
                                   {
                                      sum=x.cd.cdin_ActMortgageAmnt ?? 0
                                   }).ToList()

这里有一个方法：

var summ = db.Companies.Join(
    db.CDIndexes,
    cd => cd.cdin_CompanyId,
    com => Comp_CompanyId,
    (com, cd) => new { com, cd })
  .Where(z=>z.com.comp_idcust.Contains("10319")) // Added "LIKE"
  .Where(z=>z.cd.cdin_Status == "InProgress")
  .Where(z=>z.cd.cdin_startunstufdate != null) // Reversed your condition
  .Where(z=>z.cd.cdin_Deleted == null)
  .Sum(z=>z.cd.cdin_ActMortgageAmnt);

您也可以将所有位置组合在一起，但我不希望在大多数情况下这样：

var sumation = (from com in db.Companies
                join cd in db.CDIndexes on com.Comp_CompanyId equals cd.cdin_CompanyId
                where
                    cd.cdin_Status == "InProgress" &&
                    cd.cdin_startunstufdate == null &&
                    cd.cdin_Deleted == null
                select new {
                    sum = cd.cdin_ActMortgageAmnt 
                }
               );

var summ = sumation.Sum(x => x.sum);

var summ = db.Companies.Join(
    db.CDIndexes,
    cd => cd.cdin_CompanyId,
    com => Comp_CompanyId,
    (com, cd) => new { com, cd })
  .Where(z=>z.com.comp_idcust.Contains("10319") // Added "LIKE"
    && z.cd.cdin_Status == "InProgress" 
    && z.cd.cdin_startunstufdate != null // Reversed your condition
    && z.cd.cdin_Deleted == null)
  .Sum(z=>z.cd.cdin_ActMortgageAmnt);

---

当你指向它时，是var Sum。。。在活动行中划线，或者当您观察到null时，您是否已经跨过它？可能重复@KennethK。我所做的就是按F5键，跟踪点变为黄色箭头，调试器点击var summ，这样我按F11键执行一行，然后我指向var summ，它显示summ | nullCompare:cdin_startunstufdate不为null，cd.cdin_startunstufdate==null。你甚至不想用comp_idcust过滤。您的两个查询SQL和LINQ完全不同。@Jamiec非常感谢，我将两个查询处理为相同的。`select new{cddd=cd.cdin\u ActMortgageAmnt==null？0:cd.cdin\u ActMortgageAmnt}；`这是否解决了空值的问题？这只是为cdin_ActMortgageAmnt提供了一个默认值，在本例中为0，或者为case和查询中的值。如果仍然为null，则是因为数据不符合指定的条件。另外，您的like语句应该使用Contains comp_idcust进行转换。CONTAINS10319合并不是问题，因为总和只会忽略空值，因此无需事先确保将空值转换为0。问题很可能是他的查询查找的是din_startunstufdate==null而不是！=null，就像他的SQL正在做的一样。Close，但您已经反转了com=>com.Comp_CompanyId，cd=>cd.cdin_CompanyId，，，并且不需要.ToList。@RobertMcKee我是如何反转的？应该是cd=>cd.cdin_CompanyId，com=>com.Comp_CompanyId，内键选择，然后外键您反转了@RobertMcKee answer上的语句，唯一的添加内容是select，这没有道理。复制,paset@Zinov实际上，在我发布我的答案之前，他已经发布了他的答案，所以他没有复制/粘贴我的答案。这是一个很好的答案，只是一些小问题。此外，公司应该在您的模型中具有CDIndexes的导航属性，这将使此查询非常简单。