Question

我花了最近两个小时研究这个。 LINQ btw是新手。如何将这样的SQL转换为LINQ查询？

SELECT      r.id, name, designation, COUNT(a.id)
FROM        region r
LEFT JOIN   area a on a.region_id = r.id
GROUP BY    r.id, name, designation

我当然可以选择将其置于View（我可以弄清楚）中，但我想将此添加到我的知识中。谢谢！

P.S。 VB或C＃都可以，但我更喜欢前者。

Answer 1

我认为会是这样的：

var result =
            from r in regions
            join a in areas on r.id equals a.region_id into subvalues
            select new { id = r.id, name = r.name, designation = r.designation, count = subvalues.Count() };

Answer 2

假设您要对数据进行分组，请尝试查看类似于以下内容的查询：

account         invoicedate ageamount
1-129285408641  2016-02-08  92
1-129285650772  2016-02-08  666
1-129285408641  2016-07-08  717
1-129285650772  2016-07-08  885
1-129285650772  2015-09-08  766
1-129285408641  2016-05-08  1479
1-129285650772  2016-05-08  637
1-129285650772  2015-10-08  682
1-129285408641  2016-03-08  668
1-129285650772  2016-01-08  637
1-129285650772  2015-08-08  439
1-129285650772  2015-12-08  641
1-129285650772  2015-07-08  109
1-129285408641  2016-06-08  183
1-129285650772  2016-06-08  914
1-129285650772  2016-08-08  415
1-129285408641  2016-08-08  1198
1-129285650772  2016-10-08  579
1-129285408641  2016-11-08  250
1-129285650772  2016-11-08  1148
1-129285650772  2015-11-08  694
1-129285408641  2015-09-08  1363
1-129285650772  2016-03-08  748
1-129285408641  2016-01-08  1347
1-129285408641  2015-11-08  442
1-129285408641  2015-08-08  409
1-129285408641  2015-12-08  918
1-129285408641  2015-07-08  109
1-129285408641  2016-04-08  421
1-129285650772  2016-04-08  637
1-129285650772  2016-09-08  1000
1-129285408641  2016-09-08  119
1-129285408641  2016-10-08  1228

Answer 3

这样的事也可以正常工作..

int count = 0;

(from r in region
join a in area on r.<join_val> equals a.<join_val> into leftJ
from lj in leftJ.DefaultIfEmpty()
select lj
).GroupBy( r => r.id).All(item => 
{ 
count += item.Count();
return true;
});

count应具有您正在寻找的值，

LINQ的简单SQL计数？

3 个答案: