1、 查询Student表中的所有记录的Sname、Ssex和Class列。(select sname,ssex,class from student)
Students.Select(s=> new { sname=>s.sname,ssex=>s.ssex, class=>s.class})
linq:from s in Students select new{s.sname, }

2.查询教师所有的单位即不重复的Depart列。select distinct depart from teacher
teachers.distinct().Select(s=>s.depart)
linq: from s in teachers.Distinct() select s.depart

3、 查询Student表的所有记录。select * from Student
student.Select(s=>s)
linq: from s in student select s;

4、 查询Score表中成绩在60到80之间的所有记录。 select * from score where grages bewteen 60 and 80
score.Where(s=>(s.grages>60 && s.grages<80) );
linq: from s in score where s.grages>60 && s.grages<80 select s;

5、 查询Score表中成绩为85，86或88的记录。select * from score where grages in (85,86,88)
linq: from s in Score Where ( new decimal[] {85,86,88}.Contains(s.grage))
Scores.Where( s => new Decimal[] {85,86,88}.Contains(s.grage))

6、 查询Student表中"95031"班或性别为"女"的同学记录。select * from student where class ='95031' or ssex= '女'
student.Where(s=> （s.class=="95031" || s.sex="女"）)
from s in student where s.class=="" || s.sex=="" select s;

7、 以Class降序查询Student表的所有记录。 select * from student order by Class DESC
student.OrderByDescing(s=> s.Class)

from s in student order by s.class descending select s;

8、 以Cno升序、Degree降序查询Score表的所有记录。select * from Score order by cno asc and grage desc
score.OrderByDescing(s=>s.grage).OrderBy(s=>s.cno);

from s in score order by s.grage descending order by s.cno ascending select s;

9、 查询"95031"班的学生人数。select count(*) from Students where class='95031'
students.Select(s=>s.class=='95031').Count();
///students.Where(s=>s.class=='').Select(s=>s).Count();

10、查询Score表中的最高分的学生学号和课程号。

11、查询'3-105'号课程的平均分。select avg(grage) from score where cno='3-105'
score.where(s=>s.con=="3-105").Select(s=>s.grage).Avgage();

12、查询Score表中至少有5名学生选修的并以3开头的课程的平均分数。
select avg(degree) from score where cno like '3%' group by Cno having count(*)>=5

linq: from s in score where s.con.StartWith("3") group s by s.Cno into cc where cc.count>5
select cc.Avgage(s=>s.grage)

13、查询最低分大于70，最高分小于90的Sno列。select Sno from score group by Sno having min(grage)>70 and
max(grage)<90
linq: from s in score group s by s.sno into cc where cc.min(grage)>70 && cc.Max(grage)<90
select new {sno =>cc.key}

lambda:
scores.GroupBy(s=>s.sno).Where(ss=> ( (ss.Min(cc=>cc.grage)>70) && (ss.Max(cc=>cc.grage)<90 )))
.select(ss=> new {sno=>ss.key})

14、查询所有学生的Sname、Cno和Degree列。
select s.sname,sc.cno,sc.degree from student s,score sc where s.sno = sc.sno

from s in Student join sc in score on s.sno=sc.sno
select new {s.sname,sc.cno, sc.degree}

lambda: Student.join(scores,s=>s.sname,
sc=>sc.cno,
(s,sc)=> new{ sname =s.sname, cno=sc.cno, degree=sc.degree })

//释放资源 .Dispose();
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.skip(1).Take(4) Skip 上面这段语句的意思是从第二条数据开始显示4条
AppendAndWhere //附加AND查询条件 JoinOnAndWhere //joinon筛选条

Any(): 判断集合中是否有元素满足某一条件
仅返回没有订单的客户：var q =from c in db.Customers where !c.Orders.Any()　select c;

All(): 判断集合中所有元素是否都满足某一条件。
var q =from c in db.Customers where c.Orders.All(o => o.ShipCity == c.City) select c;
语句描述：这个例子返回所有订单都运往其所在城市的客户或未下订单的客户。

Contains() :用于判断集合中是否包含有某一元素

Concat(连接)： 连接不同的集合，不会自动过滤相同项
var q = (from c in db.Customers select c.Phone).Concat(from c in db.Customers select c.Fax).Concat(from e in db.Employees select e.HomePhone);
语句描述：返回所有消费者和雇员的电话和传真。

Union :：连接不同的集合，自动过滤相同项；延迟。即是将两个集合进行合并操作，过滤相同的项。

Intersect(相交) ：取相交项；延迟。即是获取不同集合的相同项（交集）。
Except (与非) ：排除相交项；
.Implicit（隐式） Explicit（显式）

ToArray：将序列转换为数组

ToList：将序列转换为泛型列表
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