Linq(急！)
0
[已解决问题]
解决于 2008-11-08 12:24
原sql:
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 to Sql：
(
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.ToString()
let cno = from ssss in Scores
where ssss.DEGREE == maxDegree
select ssss.CNO.ToString()
where sno == s.SNO
select new {
s.SNO,
c.CNO
}
).Distinct()
运行时：
报错：运算符“==”无法应用于“System.Linq.IQueryable<string>”和“string”类型的操作数
如何调整一下linq to sql ?
最佳答案
0
你可以这样
(
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()
其他回答(1)
0
问题应该处在sno==s.SNO上，由于你的sno是from出来的，所以是IQueryable类型，对于IQueable类型我记得有个扩展方法叫.Unique还是叫.Single，反正就那意思，具体是什么我好久没玩linq了，也忘了，你让let sno = Scores.Single(ssss => ssss.Degree == MaxDegree).CNO.ToString()的话，应该就可以选出来了。
具体思路就是这样吧，由于我很久没玩linq，手上也没有你的实体类定义，所以只能给出这样的解答了。呵呵