sql linq lambda 对比
时间：2021-07-01 10:21:17
帮助过：2人阅读
、 查询Student表中的所有记录的Sname、Ssex和Class列。
select sname,ssex,
class from student
Linq:
from s
in Students
select new {
s.SNAME,
s.SSEX,
s.CLASS
}
Lambda:
Students.Select( s =>
new {
SNAME = s.SNAME,SSEX = s.SSEX,CLASS =
s.CLASS
})
2、 查询教师所有的单位即不重复的Depart列。
select distinct depart
from teacher
Linq:
from t
in Teachers.Distinct()
select t.DEPART
Lambda:
Teachers.Distinct().Select( t =>
t.DEPART)
3、 查询Student表的所有记录。
select *
from student
Linq:
from s
in Students
select s
Lambda:
Students.Select( s =>
s)
4、 查询Score表中成绩在60到80之间的所有记录。
select *
from score
where degree between
60 and
80
Linq:
from s
in Scores
where s.DEGREE >=
60 && s.DEGREE <
80
select s
Lambda:
Scores.Where(
s =>
(
s.DEGREE >=
60 && s.DEGREE <
80
)
)
5、 查询Score表中成绩为85，86或88的记录。
select *
from score
where degree
in (
85,
86,
88)
Linq:
In
from s
in Scores
where (
new decimal[]{
85,
86,
88}
).Contains(s.DEGREE)
select s
Lambda:
Scores.Where( s =>
new Decimal[] {
85,
86,
88}.Contains(s.DEGREE))
Not in
from s
in Scores
where !
(
new decimal[]{
85,
86,
88}
).Contains(s.DEGREE)
select s
Lambda:
Scores.Where( s => !(
new Decimal[]{
85,
86,
88}.Contains(s.DEGREE)))
Any()应用：双表进行Any时，必须是主键为(String)
CustomerDemographics CustomerTypeID（String）
CustomerCustomerDemos (CustomerID CustomerTypeID) (String)
一个主键与二个主建进行Any(或者是一对一关键进行Any)
不可，以二个主键于与一个主键进行Any
from e
in CustomerDemographics
where !
e.CustomerCustomerDemos.Any()
select e
from c
in Categories
where !
c.Products.Any()
select c
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= N
‘女‘
Linq:
from s
in Students
where s.CLASS ==
"95031"
|| s.CLASS ==
"女"
select s
Lambda:
Students.Where(s => ( s.CLASS ==
"95031" || s.CLASS ==
"女"))
7、 以Class降序查询Student表的所有记录。
select *
from student order by Class DESC
Linq:
from s
in Students
orderby s.CLASS descending
select s
Lambda:
Students.OrderByDescending(s =>
s.CLASS)
8、 以Cno升序、Degree降序查询Score表的所有记录。
select *
from score order by Cno ASC,Degree DESC
Linq:(这里Cno ASC在linq中要写在最外面)
from s
in Scores
orderby s.DEGREE descending
orderby s.CNO ascending
select s
Lambda:
Scores.OrderByDescending( s =>
s.DEGREE)
.OrderBy( s =>
s.CNO)
9、 查询
"95031"班的学生人数。
select count(*)
from student
where class =
‘95031‘
Linq:
( from s
in Students
where s.CLASS ==
"95031"
select s
).Count()
Lambda:
Students.Where( s => s.CLASS ==
"95031" )
.Select( s =>
s)
.Count()
10、查询Score表中的最高分的学生学号和课程号。
select distinct s.Sno,c.Cno
from student
as s,course
as c ,score
as sc
where s.sno=(
select sno
from score
where degree = (
select max(degree)
from score))
and c.cno = (
select cno
from score
where degree = (
select max(degree)
from score))
Linq:
(
from s
in Students
from c
in Courses
from sc
in Scores
let maxDegree = (
from sss
in Scores
select sss.DEGREE
).Max()
let sno = (
from ss
in Scores
where ss.DEGREE ==
maxDegree
select ss.SNO).Single().ToString()
let cno = (
from ssss
in Scores
where ssss.DEGREE ==
maxDegree
select ssss.CNO).Single().ToString()
where s.SNO == sno && c.CNO ==
cno
select new {
s.SNO,
c.CNO
}
).Distinct()
操作时问题？执行时报错： where s.SNO == sno（这行报出来的） 运算符
"=="无法应用于
"string"和
"System.Linq.IQueryable<string>"类型的操作数
解决：
原：let sno = (
from ss
in Scores
where ss.DEGREE ==
maxDegree
select ss.SNO).ToString()
Queryable().Single()返回序列的唯一元素；如果该序列并非恰好包含一个元素，则会引发异常。
解：let sno = (
from ss
in Scores
where ss.DEGREE ==
maxDegree
select ss.SNO).Single().ToString()
11、查询
‘3-105‘号课程的平均分。
select avg(degree)
from score
where cno =
‘3-105‘
Linq:
(
from s
in Scores
where s.CNO ==
"3-105"
select s.DEGREE
).Average()
Lambda:
Scores.Where( s => s.CNO ==
"3-105")
.Select( s =>
s.DEGREE)
.Average()
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 Scores
where s.CNO.StartsWith(
"3")
group s by s.CNO
into cc
where cc.Count() >=
5
select cc.Average( c =>
c.DEGREE)
Lambda:
Scores.Where( s => s.CNO.StartsWith(
"3") )
.GroupBy( s =>
s.CNO )
.Where( cc => ( cc.Count() >=
5) )
.Select( cc => cc.Average( c =>
c.DEGREE) )
Linq: SqlMethod
like也可以这样写:
s.CNO.StartsWith("3") or SqlMethods.Like(s.CNO,
"%3")
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(degree) >
70 and max(degree) <
90
Linq:
from s
in Scores
group s by s.SNO
into ss
where ss.Min(cc => cc.DEGREE) >
70 && ss.Max( cc => cc.DEGREE) <
90
select new
{
sno =
ss.Key
}
Lambda:
Scores.GroupBy (s =>
s.SNO)
.Where (ss => ((ss.Min (cc => cc.DEGREE) >
70) && (ss.Max (cc => cc.DEGREE) <
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
as s,score
as sc
where s.sno =
sc.sno
Linq:
from s
in Students
join sc in Scores
on s.SNO equals sc.SNO
select new
{
s.SNAME,
sc.CNO,
sc.DEGREE
}
Lambda:
Students.Join(Scores, s =>
s.SNO,
sc =>
sc.SNO,
(s,sc) =>
new{
SNAME =
s.SNAME,
CNO =
sc.CNO,
DEGREE =
sc.DEGREE
})
15、查询所有学生的Sno、Cname和Degree列。
select sc.sno,c.cname,sc.degree
from course
as c,score
as sc
where c.cno =
sc.cno
Linq:
from c
in Courses
join sc in Scores
on c.CNO equals sc.CNO
select new
{
sc.SNO,c.CNAME,sc.DEGREE
}
Lambda:
Courses.Join ( Scores, c =>
c.CNO,
sc =>
sc.CNO,
(c, sc) =>
new
{
SNO =
sc.SNO,
CNAME =
c.CNAME,
DEGREE =
sc.DEGREE
})
16、查询所有学生的Sname、Cname和Degree列。
select s.sname,c.cname,sc.degree
from student
as s,course
as c,score
as sc
where s.sno = sc.sno and c.cno =
sc.cno
Linq:
from s
in Students
from c
in Courses
from sc
in Scores
where s.SNO == sc.SNO && c.CNO ==
sc.CNO
select new { s.SNAME,c.CNAME,sc.DEGREE }
转自CSDN：http://blog.csdn.net/swarb/article/details/8206976
sql linq lambda 对比
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