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.
--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
left join 左连接即以左表为基准,显示坐标所有的行,右表与左表关联的数据会显示,不关联的则不显示.关键字为left join on. **基本用法如下: select table a left join table b on a.id = b.ta_id** 注意:1⃣️其中on后面关联的字段应该是同一字段(两表关联的外键) 2⃣️由于以左表为基准,左表一条记录如果对应右表多条记录,那查出的数据中右表的数据也只显示一条,如果要都显示,可以用group_contact()将字段用逗号隔开显
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
.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
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
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
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
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
格式 select f1.a, f2.b form f1 left jion f2 on .... 注意:左边的查询部分只能有select和from,不能出现where order by等.若有必须在外嵌套一层 select On 后面的条件只影响入选的f2.b字段有没有值,不影响总行数 (2016.9.9 上面说法错误!可以写where和order,写在on语句之后就行) 2017.10.25 两张表都带where条件的left join 写法 写法1: 左表的where条件写在on语句后,右
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
select * from A表 a left join B表 b on a.id=b.a_id and b.字段='/*条件*/' ; 可查出左表所有数据 select * from A表 a left join B表 b on a.id=b.a_id where b.字段='/*条件*/' ; 只能查出部分数据
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
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 {
