前提：一个学生表Student，一个描述表Desc

表数据：

表数据

left join：

sql：

SELECT * FROM Student

                  LEFT JOIN [Desc]

                  ON Student.ID=[Desc].ID

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linq：

读取全部：

from student in db.Student join desc in db.Desc on student.ID equals desc.StudentID into jointemp from temp in jointemp.DefaultIfEmpty() select new { student, temp };

读取指定字段：

from student in db.Student join desc in db.Desc on student.ID equals desc.StudentID into jointemp from temp in jointemp.DefaultIfEmpty()select new{ID =student.ID,Name =student.Name,Mark =temp.Mark};

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lambda：

读取全部：

db.Student.GroupJoin(db.Desc, u => u.ID, d => d.StudentID, (u, d) => new { u, d }).Select(o => o)；

读取指定字段：

db.Student.GroupJoin(db.Desc, u => u.ID, d => d.StudentID, (u, d) => d.DefaultIfEmpty().Select(p => new {ID=u.ID,Name=u.Name,Mark=p.Mark })).SelectMany(o => o);

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right join：

SELECT * FROM Student

RIGHTJOIN [Desc]

ON Student.ID=[Desc].ID

PS：A left join B=B right join A

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对应linq以及lambda即调换两个表位置

inner join：

SELECT * FROM Student

INNER JOIN [Desc]

ON Student.ID=[Desc].ID

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linq:

读取全部：

from student in db.Student join desc in db.Desc on student.ID equals desc.StudentID select new { student, desc };

读取指定字段：

from student in db.Student join desc in db.Desc on student.ID equals desc.StudentID select new { ID = student.ID, Name = student.Name, Mark = desc.Mark };

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lambda:

读取全部：

db.Student.Join(db.Desc, u => u.ID, d => d.StudentID, (u, d) => new { u, d }).Select(o => o);

读取指定字段：

db.Student.Join(db.Desc, u => u.ID, d => d.StudentID, (u, d) =>new { ID = u.ID, Name = u.Name, Mark = d.Mark }).Select(o => o);

full join：

SELECT * FROM Student

FULL JOIN [Desc]

ON Student.ID=[Desc].ID

corss join：

SELECT * FROM Student

CORSS JOIN [Desc]

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linq：

读取全部

from student in db.Student from desc in db.Desc select new { student, desc };

读取指定字段

from student in db.Student from desc in db.Desc select new { ID = student.ID, Name = student.Name, Mark = desc.Mark };

lambda：

读取全部

读取指定字段