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…

通常情况下我们在做leftjoin连接时需要对不止一个条件进行进行匹配,这时候就需要使用闭包方式,如下: leftjoin('db', function ($join) {···}); leftjoin多条件查询,无非以下三种情况. 并且关系(&&)且为字段名称,使用on,代码示例如下: $roomUuid = 1; $chatInfo = DB::table('chat_info') ->where('chat_info.room_uuid', $roomUuid) ->le…