Linq groupjoin 左连接

LINQ的左连接、右连接、内连接和Lamda表达式实现Left join

1.左连接: var LeftJoin = from t1 in l1join t2 in l2on t1.ID equals t2.ID into Joinedt12from t3 in Joinedt12.DefaultIfEmpty()select new {Name = t1.Name,Age=t2.Age }; 2.右连接: var RightJoin = from t2 in l2join t

Linq实现左连接、右连接

--一本错误的记录 insert into Book values('错误时怎样练成的',111) --左连接 select s.name,b.name from student as s left join Book as b on s.id=b.studentid --右连接 select s.name,b.name from student as s right join Book as b on s.id=b.studentid 要用Linq实现左连接,写法如下

Lambda方式左连接有Linq方式左连接

网上查到的直接使用Join+DefaultIfEmpty的方式是错误的,实际生成SQL是两表先内联接,然后再LEFT JOIN.经过查证,参考资料,最终得到如下两种方式的左连接写法: public void TestMethod1() { MettingEntities db = new MettingEntities(); //LINQ方式 var query = (from st in db.met_SysItemsClass join cl in db.met_Shortcut on st

LINQ的左连接、右连接、内连接

.左连接: var LeftJoin = from emp in ListOfEmployees join dept in ListOfDepartment on emp.DeptID equals dept.ID into JoinedEmpDept from dept in JoinedEmpDept.DefaultIfEmpty() select new { EmployeeName = emp.Name, DepartmentName = dept != null ? dept.Name

linq实现左连接

1.左连接: var LeftJoin = from emp in ListOfEmployees join dept in ListOfDepartment on emp.DeptID equals dept.ID into JoinedEmpDept from dept in JoinedEmpDept.DefaultIfEmpty() select new { EmployeeName = emp.Name, DepartmentName = dept != null ? dept.Na

linq 之左连接

List<ArticleModel> articleList = articleRepository.GetAllArticle(); List<UsersModel> userList = usersRepository.GetAllUsers(); //用户表左连接文章表 var usersLeftJoin = (from u in userList join a in articleList on u.Id equals a.Author into users from us

linq的左连接右连接内连接用法

1.左连接: var LeftJoin = from e in ListOfEmployees join d in ListOfDepartment on e.DeptID equals d.ID into JoinedEmpDept from d in JoinedEmpDept.DefaultIfEmpty() select new { EmployeeName = e.Name, DepartmentName = d!= null ? d.Name : null }; 2.右连接: var

linq之左连接 + group by

var list = from item in (from s in _sysBll.GetList(s => s.ParamID == "TraSchType" && s.ParamCode != null) join t in data on s.ParamCode equals t.TraSchType into tmp from f in tmp.DefaultIfEmpty() select new { value = tmp.Count(), name

linq join 左连接 leftjoin 多个on条件 where 条件

var haveChange = from newScore in newScoreList join oldScore in oldScoreList on new{newScore.ExamId,newScore.StudentId,newScore.Subject,newScore.ClassId} equals new{oldScore.ExamId,oldScore.StudentId,oldScore.Subject,oldScore.ClassId} where newScore.

Linq Left Join；linq左连接（转载）

来源 https://www.cnblogs.com/xinjian/archive/2010/11/17/1879959.html 准备一些测试数据,如下: use Test Create table Student( ID int identity(1,1) primary key, [Name] nvarchar(50) not null ) Create Table Book( ID int identity(1,1) primary key, [Name] nvarchar(50)no

LINQ中的连接(join)用法示例

Linq中连接主要有组连接.内连接.左外连接.交叉连接四种.各个用法如下. 1. 组连接组连接是与分组查询是一样的.即根据分组得到结果. 如下例,根据publisther分组得到结果. 使用组连接的查询语句如下: //使用组连接 var GroupQuery = from publisher in SampleData.Publishers join book in SampleData.Books on publisher equals book.Publisher into publish

Linq to Sql 左连接 , 取右表可能为 null的 int类型字段

linq to sql , linq to entity 遇到一个问题, 主表, 从表一对一关系, 主表有记录, 从表可能没有记录. 现在要查询主表+从表的某几个字段. 从表字段有的是 Tzsbh int? 类型. int 转 string 如果对象为null,报错 var queryLeft = from c in db.AA join sr in ( from ss in db.BB select ss ) on c.Id equals sr.Sid into x f

Linq连接查询之左连接、右连接、内连接、全连接、交叉连接、Union合并、Concat连接、Intersect相交、Except与非查询

内连接查询内连接与SqL中inner join一样,即找出两个序列的交集 Model1Container model = new Model1Container(); //内连接 var query = from s in model.Student join c in model.Course on s.CourseCno equals c.Cno select new { ClassID = s.CourseCno, ClassName = c.Cname, Student = new {

EF Linq中的左连接Left Join查询

linq中的join是inner join内连接,就是当两个表中有一个表对应的数据没有的时候那个关联就不成立. 比如表A B的数据如下 from a in A join b in B on a.BId equals b.Idselect new {a.Id, b.Id} 的结果是 {1,1} {2,2} {4,4} 因为3在B表中不存在,所以连接失败,不返回,但是当我们需要返回一个{3, null}的时候怎么办呢,这就是左连接,反之,如果是{null,3} 则是右连接. from a in A

GroupBy分组的运用和linq左连接

最简单的分组 var conHistoryList = conHistoryData.GroupBy(g => g.personId); 就是conHistoryData是一个IQueryable<T>类型: 分组后组内排序 var conHistoryList = conHistoryData.GroupBy(g => g.personId).Select(g => g.OrderBy(c => c.addTime)); 对数据分组之后在根据每一个分组内的某一个元素排

Linq 和 SQL的左连接、右连接、内链接

在我们工作中表连接是很常用的,但常用的有这三种连接方式:左连接.右连接.内链接在本章节中讲的是1.如何在Linq中使用左连接,右连接,内连接. 2.三种连接之间的特点在哪? 3.Linq的三种连接语法是怎么样的呢(我觉得左右连接也就相当换个位置) 一.SQL Server 中的三种连接首先我们示范以下SQL中的左连接,右连接,内连接,需要准备两张表: CREATE TABLE [dbo].[Company]( [Id] int identity Primary key, [Code] uni

linq to entity 左连接右连接以及内连接写法的区别

左连右连还是内连这个其实你不需要关心.只需要根据实体的映射关系写查询,框架会自动帮你生成的. 至于linq查询语法与扩展方法的效率,应该是一样的,比如: var users=(from u in db.Users where u.UserRoleId==1 select u) .ToList(); var users2=db.Users.Where(u=>u.UserRoleId==1).ToList(); 这两句查询实际上是等效的. inner join: var =from x in d

C# linq左连接与分组

1.左连接使用DefaultIfEmpty(): 2.分组时候判断newper.FirstOrDefault() == null ? null: newper.ToList()这个经常出错误,如果不判断,会出现空引用的错误 class Program { class Person { public string FirstName { get; set; } public string LastName { get; set; } } class Pet { public string Name

linq 左连接后实现与主表一对一关系数据

var query1 = from r in _residentRepository.GetAll() join i in _inLogRepository.GetAll() on r.Id equals i.ResidentId into tmp_ir from ir in tmp_ir.DefaultIfEmpty() || r.Id == select new { resId = r.Id, Id = ir.Id }; var sum1 = query1.Count(); 结果:左连接一

EF to linq 左连接

如果连接的数据不存在用 null 表示,则可以左连接查询,但是如果数据类型为 int 则会出错. var ng = (from g in _db.NET_NEWS_GROUP join z in _db.NET_NEWS_GROUP_INFO on g.NET_NEWS_GROUP_ID equals z.NET_NEWS_GROUP_ID into nglist from n in nglist.DefaultIfEmpty() select new { NET_NEWS_GROUP_ID =

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