我用谷歌搜索并尝试了很多这里找到的样本，但我无法让它发挥作用。
我有以下SQL代码
Declare @PO as table
(Id int,
Date datetime,
PoNumber nvarchar(10),
CustomerName nvarchar(100))
Insert Into @PO values (1, '2013-07-15', 'po-01', 'Customer AAA')
Insert Into @PO values (1, '2013-07-15', 'po-02', 'Customer BBB')
Insert Into @PO values (1, '2013-07-15', 'po-03','Customer CCC')
Declare @SH as table
(Id int,
Date datetime,
PoNumber nvarchar(10),
ShNumber nvarchar(10),
DocumentType int)
Insert into @SH values (1, '2013-07-20', 'po-01', 'sh-01', 1)
Insert into @SH values (2, '2013-07-20', 'po-03', 'sh-02', 1)
Declare @SD as table
(Id int,
Qty int,
DocumentType int,
ShNumber nvarchar(10),
ShippingDate datetime)
Insert Into @SD values (1,1,1,'sh-01', '2013-08-01')
Insert Into @SD values (2,2,2,'sh-01', '2013-08-02')
Insert Into @SD values (3,1,1,'sh-01', '2013-08-03')
Insert Into @SD values (4,2,2,'sh-01', '2013-08-04')
Insert Into @SD values (5,1,1,'sh-01', '2013-08-05')
Insert Into @SD values (6,3,1,'sh-02', '2013-08-06')
Insert Into @SD values (7,1,1,'sh-02', '2013-08-07')
Insert Into @SD values (8,2,2,'sh-02', '2013-08-08')
Insert Into @SD values (9,1,2,'sh-02', '2013-08-09')
Select PO.PoNumber, CustomerName, Isnull(SH.ShNumber,''), Max(ShippingDate) ShippingDate, Sum(Isnull(SD.Qty,0)) QuantitySold From @PO PO
left join @SH SH
on PO.PoNumber = SH.PoNumber
left join @SD SD on SH.ShNumber = SD.ShNumber and SH.DocumentType = SD.DocumentType
group by PO.PoNumber, CustomerName, SH.ShNumber
order by PO.PoNumber
正确返回
po-01 Customer AAA sh-01 2013-08-05 00:00:00.000 3
po-02 Customer BBB NULL 0
po-03 Customer CCC sh-02 2013-08-07 00:00:00.000 4
使用精彩的LinqPad，我尝试做同样的事情。
我创建了3个类
public class PO
{
public int Id { get; set; }
public DateTime Date { get; set; }
public string PoNumber { get; set; }
public string CustomerName { get; set; }
}
public class SH
{
public int Id { get; set; }
public DateTime Date { get; set; }
public string PoNumber { get; set; }
public string ShNumber { get; set; }
public int Documenttype { get; set; }
}
public class SD
{
public int Id { get; set; }
public int Qty { get; set; }
public int DocumentType { get; set; }
public string ShNumber { get; set; }
public DateTime ShippingDate { get; set; }
}
然后创建了我的sql添加的相同测试日期
var po = new List<PO>();
var sh = new List<SH>();
var sd = new List<SD>();
po.Add(new PO() {Id=1,Date = new DateTime(2013,7,15), PoNumber = "po-01", CustomerName = "Customer AAA"});
po.Add(new PO() {Id=2,Date = new DateTime(2013,7,15), PoNumber = "po-02", CustomerName = "Customer BBB"});
po.Add(new PO() {Id=3,Date = new DateTime(2013,7,15), PoNumber = "po-03", CustomerName = "Customer CCC"});
sh.Add(new SH() {Id=1, Date = new DateTime(2013,7,20), PoNumber = "po-01", ShNumber = "sh-01", Documenttype= 1});
sh.Add(new SH() {Id=2, Date = new DateTime(2013,7,20), PoNumber = "po-03", ShNumber = "sh-02", Documenttype= 1});
sd.Add(new SD() {Id=1, ShippingDate = new DateTime(2013,8,1), ShNumber = "sh-01", DocumentType = 1, Qty = 1});
sd.Add(new SD() {Id=2, ShippingDate = new DateTime(2013,8,2), ShNumber = "sh-01", DocumentType = 2, Qty = 2});
sd.Add(new SD() {Id=3, ShippingDate = new DateTime(2013,8,3), ShNumber = "sh-01", DocumentType = 1, Qty = 1});
sd.Add(new SD() {Id=4, ShippingDate = new DateTime(2013,8,4), ShNumber = "sh-01", DocumentType = 2, Qty = 2});
sd.Add(new SD() {Id=5, ShippingDate = new DateTime(2013,8,5), ShNumber = "sh-01", DocumentType = 1, Qty = 1});
sd.Add(new SD() {Id=6, ShippingDate = new DateTime(2013,8,6), ShNumber = "sh-02", DocumentType = 1, Qty = 3});
sd.Add(new SD() {Id=7, ShippingDate = new DateTime(2013,8,7), ShNumber = "sh-02", DocumentType = 1, Qty = 1});
sd.Add(new SD() {Id=8, ShippingDate = new DateTime(2013,8,8), ShNumber = "sh-02", DocumentType = 2, Qty = 2});
sd.Add(new SD() {Id=9, ShippingDate = new DateTime(2013,8,9), ShNumber = "sh-02", DocumentType = 2, Qty = 1});
然而，当我尝试重现相同的逻辑来查询该数据时，我迷失了第二个左连接及其组
这是我停止的地方
var query = from p in po
join h in sh
on p.PoNumber equals h.PoNumber into j2
from j3 in j2.DefaultIfEmpty()
group j3 by new {CustomerName = p.CustomerName, PoNumber = p.PoNumber, DocumentType = j3 == null ? 0 : j3.Documenttype, ShNumber = j3 == null ? string.Empty : j3.ShNumber}
into grouped
join d in sd
on new {grouped.Key.ShNumber, grouped.Key.DocumentType} equals new {d.ShNumber, d.DocumentType} into k2
from k3 in k2.DefaultIfEmpty()
group new {k3.ShippingDate, k3.Qty} by new {grouped.Key.ShNumber, grouped.Key.CustomerName, grouped.Key.PoNumber} into g2
select new {
PoNumber = g2.Key.PoNumber,
CustomerName = g2.Key.CustomerName,
ShNumber = g2.Key.ShNumber,
Qty = g2.Sum(o => o.Qty),
ShippingDate = g2.Max(o => o.ShippingDate)
};
如果有人可以提供帮助，那将非常感激。
答案 0 :(得分：2)
我想通了。我必须在结束时做Sum和Max时检查空值
var query = from p in po
join h in sh
on p.PoNumber equals h.PoNumber into j2
from j3 in j2.DefaultIfEmpty()
group j3 by new {CustomerName = p.CustomerName, PoNumber = p.PoNumber, DocumentType = j3 == null ? 0 : j3.Documenttype, ShNumber = j3 == null ? string.Empty : j3.ShNumber}
into grouped
join d in sd
on new {grouped.Key.ShNumber, grouped.Key.DocumentType} equals new {d.ShNumber, d.DocumentType} into k2
from k3 in k2.DefaultIfEmpty()
group k3 by new {ShNumber= grouped.Key.ShNumber, CustomerName = grouped.Key.CustomerName, PoNumber = grouped.Key.PoNumber} into g2
select new {
PoNumber = g2.Key.PoNumber,
CustomerName = g2.Key.CustomerName,
ShNumber = g2.Key.ShNumber,
Qty = g2.Sum(o => o == null ? 0 : o.Qty),
ShippingDate = g2.Max(o => o == null ? DateTime.MinValue : o.ShippingDate)
};