Question

您好我正在编写linq查询以获取两个表中的列的最大计数。我写了sql查询，它在下面。

select MAX(p.dispalyOrder) from NCT_Process p INNER JOIN NCT_Process_Settings s ON 
p.projectId =s.projectId AND p.level=s.level

我试着如下所示。

dbObject = (from c in entityObject.NCT_Process_Settings
            join process in entityObject.NCT_Process on c.projectId equals process.projectId
            join level in entityObject.NCT_Process on c.level equals level.level
            select new settingsobject
            {
                MAX(p.dispalyOrder) to some propert of settingsobject
            }).Tolist();

我不确定如何从流程表中获取最大显示顺序。任何帮助，将不胜感激。谢谢。

Answer 1

您只需选择该值，然后在查询中调用max = (from c in entityObject.NCT_Process_Settings join p in entityObject.NCT_Process on new { c.projectId, c.level } equals new { p.projectId, p.level } select p.dispalyOrder).Max();。另外，要连接多个列，您必须使用要匹配的列创建匿名类。

result = (from c in entityObject.NCT_Process_Settings
          join p in entityObject.NCT_Process 
          on new { c.projectId, c.level } equals new { p.projectId, p.level }
          group new{c,p} on 1 into grp
          select new {
              MaxDisplayOrder = grp.Max(x => x.p.dispalyOrder),
              AvgOfSomething = grp.Avgerage(x => x.c.Something),
              MinOfASum = grp.Min(x => x.p.SomeNumber + x.c.SomeOtherNumber)
          }).Single();

如果您还想要聚合其他列，则可以按常量值进行分组。

Single

请注意result = (from c in entityObject.NCT_Process_Settings join p in entityObject.NCT_Process on new { c.projectId, c.level } equals new { p.projectId, p.level } group p.displayOrder on c.Id into grp select new { MaxDisplayOrder = grp.Max(), Id = grp.Key }).ToList();的使用，因为常量上的group by只会产生一行。

或者，如果您只想获得按其他列分组的最大显示顺序，请执行此操作

Key

请注意，on是您在grp之后放置的内容，on是ToList之前的值的集合。在这种情况下，可能会有多个结果，因此您可以使用<Window.Resources> <Style x:Key="MyLabelStyle" TargetType="Label"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type Label}"> <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="true" CornerRadius="3"> <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/> </Border> <ControlTemplate.Triggers> <Trigger Property="IsEnabled" Value="false"> <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> </Setter.Value> </Setter> </Style> </Window.Resources>来运行查询。

如何在linq中使用聚合函数和连接？

1 个答案: