C# LINQ-Can';t在不更改多表分组的情况下向结果中添加列
假设我有一个“数据库”,定义为:C# LINQ-Can';t在不更改多表分组的情况下向结果中添加列,c#,linq,group-by,C#,Linq,Group By,假设我有一个“数据库”,定义为: // Baked goods vendors var vendor = new[] { new { ID = 1, Baker = "Pies R Us", StMnemon = "NY", Items = 8, Rating = 9 }, new { ID = 2, Baker = "Mikes Muffins", StMnemon = "CA", Items = 5, Rating = 9 }, new { ID = 3, Ba
// Baked goods vendors
var vendor = new[] {
new { ID = 1, Baker = "Pies R Us", StMnemon = "NY", Items = 8, Rating = 9 },
new { ID = 2, Baker = "Mikes Muffins", StMnemon = "CA", Items = 5, Rating = 9 },
new { ID = 3, Baker = "Best Bakers", StMnemon = "FL", Items = 2, Rating = 5 },
new { ID = 4, Baker = "Marys Baked Treats", StMnemon = "NY", Items = 8, Rating = 7 },
new { ID = 5, Baker = "Cool Cakes", StMnemon = "NY", Items = 4, Rating = 9 },
new { ID = 6, Baker = "Pie Heaven", StMnemon = "CA", Items = 12, Rating = 9 },
new { ID = 7, Baker = "Cakes N More", StMnemon = "GA", Items = 6, Rating = 8 },
new { ID = 8, Baker = "Dream Desserts", StMnemon = "FL", Items = 2, Rating = 7 }
};
// Locations
var location = new[] {
new {ID= 1, State = "New York", Mnemonic = "NY"},
new {ID= 2, State = "Massachusetts", Mnemonic = "MA"},
new {ID= 3, State = "Ohio", Mnemonic = "OH"},
new {ID= 4, State = "California", Mnemonic = "CA"},
new {ID= 5, State = "Florida", Mnemonic = "FL"},
new {ID= 6, State = "Texas", Mnemonic = "TX"},
new {ID= 7, State = "Georgia", Mnemonic = "GA" }
};
我想构建一个与SQL查询等效的查询:
SELECT State, Rating, SUM(Items) AS 'Kinds'
FROM vendor, location
WHERE vendor.StMnemon = location.Mnemonic
GROUP BY State, Rating
var result = from v in vendor
from l in location
where l.Mnemonic == v.StMnemon
group v by new { l.State, v.Rating } into grp
orderby grp.Key.Rating ascending, grp.Key.State
select new {State = grp.Key.State, Rating = grp.Key.Rating, Kinds = grp.Sum(p=>p.Items)};
foreach (var item in result)
Console.WriteLine("{0}\t{1}\t{2}", item.State, item.Rating, item.Kinds);
此查询中有两件有趣的事情:
var query = from v in vendor
join l in location
on v.StMnemon equals l.Mnemonic
orderby v.Rating ascending, l.State
select new { v, l };
var result = from q in query
group q by new {
s = q.l.State,
r = q.v.Rating
/* ==> */ , i = q.v.Items
} into grp
select new
{
State = grp.Key.s,
Rating = grp.Key.r
/* ==> */ , Kinds = grp.Sum(k => grp.Key.i)
};
这导致:
=================================
State Rating Kinds
Florida 5 2
Florida 7 2
New York 7 8
Georgia 8 6
California 9 5
California 9 12
New York 9 8
New York 9 4
=================================
鉴于,上面给出的SQL查询给出了以下结果:
=========================
State Rating Kinds
Florida 5 2
Florida 7 2
New York 7 8
Georgia 8 6
California 9 17
New York 9 12
=========================
这种差异是因为除了分组标准之外,似乎没有地方放置其他列,这当然会改变分组结果。注释掉上面代码中/*==>*/注释所指示的两行将给出与SQL结果相同的分组,但这当然会删除我想要包含的求和字段
我们如何在LINQ中对多个表进行分组,并在不更改分组结果的情况下包含其他条件?类似的内容似乎返回与SQL查询相同的结果:
SELECT State, Rating, SUM(Items) AS 'Kinds'
FROM vendor, location
WHERE vendor.StMnemon = location.Mnemonic
GROUP BY State, Rating
var result = from v in vendor
from l in location
where l.Mnemonic == v.StMnemon
group v by new { l.State, v.Rating } into grp
orderby grp.Key.Rating ascending, grp.Key.State
select new {State = grp.Key.State, Rating = grp.Key.Rating, Kinds = grp.Sum(p=>p.Items)};
foreach (var item in result)
Console.WriteLine("{0}\t{1}\t{2}", item.State, item.Rating, item.Kinds);
类似的内容似乎返回与SQL查询相同的结果:
SELECT State, Rating, SUM(Items) AS 'Kinds'
FROM vendor, location
WHERE vendor.StMnemon = location.Mnemonic
GROUP BY State, Rating
var result = from v in vendor
from l in location
where l.Mnemonic == v.StMnemon
group v by new { l.State, v.Rating } into grp
orderby grp.Key.Rating ascending, grp.Key.State
select new {State = grp.Key.State, Rating = grp.Key.Rating, Kinds = grp.Sum(p=>p.Items)};
foreach (var item in result)
Console.WriteLine("{0}\t{1}\t{2}", item.State, item.Rating, item.Kinds);
您可以在组外进行聚合:
var query = from v in vendor
join l in location
on v.StMnemon equals l.Mnemonic
orderby v.Rating ascending, l.State
select new { v, l };
var result = from q in query
group q by new {
s = q.l.State,
r = q.v.Rating
} into grp
select new
{
State = grp.Key.s,
Rating = grp.Key.r,
Kinds = grp.Sum(g => g.Items)
};
分组有点难理解-它返回一个
i分组
,该分组有一个属性-键
。该分组中的实际项目由GetEnumerator()
函数返回,该函数允许您将该组视为这些项目的集合,这意味着您可以对该组中的项目进行聚合。您可以在组外进行聚合:
var query = from v in vendor
join l in location
on v.StMnemon equals l.Mnemonic
orderby v.Rating ascending, l.State
select new { v, l };
var result = from q in query
group q by new {
s = q.l.State,
r = q.v.Rating
} into grp
select new
{
State = grp.Key.s,
Rating = grp.Key.r,
Kinds = grp.Sum(g => g.Items)
};
分组有点难理解-它返回一个i分组
,该分组有一个属性-键
。该分组中的实际项目由GetEnumerator()
函数返回,该函数允许您将该组视为这些项目的集合,这意味着您可以对该组中的项目进行聚合