如何使用Linq執行聯合，因爲我在Mysql查詢中執行

Question

這是我如何執行聯合使用不同列名的兩個不同表， *我只從第二個表中選擇日期和金額，並將null傳遞給其餘的列*

string query="select `Date`,`ItemName`,`ReqQty`, `Amount`,`TotalAmount` from ((SELECT s.`Date` ,i.`ItemName`, s.`ReqQty`,s.`Amount`,s.`TotalAmount` FROM `sale` as s join items as i on s.itemid=i.id where s.`partyId`='" + ddllist.SelectedValue.ToString() + "') Union all ((select p.date,'','','Recieved', p.`amount` as Totalamount from `OrderPayment` as p where p.`partyId`='" + ddllist.SelectedValue.ToString() + "'))) tb order by `Date`"; 

但在LINQ，我傳遞null來，我沒有列我不能創造像MySQL虛假列..提示錯誤，這裏是我的LINQ嘗試

 var query1 = (from s in lam.sales where s.PartyId == 1 select new { Date = s.Date, Itemid = s.ItemId, Qty = s.ReqQty, Amount = s.Amount, TotalAmount = s.TotalAmount }); 

     var query2 = (from q in lam.paydetails where q.partyId == 1 select new { Date =(DateTime?) q.Date, Itemid = 0, Qty = (int?)null, Amount = (int?)null, TotalAmount = q.amount }); 
     var queryresult = query1.Concat(query2); 

銷售類

public partial class sale 
{ 
    public int Id { get; set; } 
    public int PartyId { get; set; } 
    public int ItemId { get; set; } 
    public Nullable<int> ReqQty { get; set; } 
    public Nullable<int> AvaibleQty { get; set; } 
    public string Desc { get; set; } 
    public Nullable<int> Amount { get; set; } 
    public string Remarks { get; set; } 
    public Nullable<System.DateTime> Date { get; set; } 
    public int TotalAmount { get; set; } 

    public virtual item item { get; set; } 
    public virtual partydetail partydetail { get; set; } 
} 

OrderPayment類

public partial class orderpayment 
{ 
    public int id { get; set; } 
    public Nullable<int> partyId { get; set; } 
    public Nullable<decimal> amount { get; set; } 
    public Nullable<System.DateTime> Date { get; set; } 
    public string Remarks { get; set; } 

    public virtual partydetail partydetail { get; set; } 
} 

itemClass時這是refencing到的itemId在銷售類

public partial class item 
{ 
    public item() 
    { 
     this.sales = new HashSet<sale>(); 
     this.ordereds = new HashSet<ordered>(); 
     this.stocks = new HashSet<stock>(); 
     this.productions = new HashSet<production>(); 
     this.productions1 = new HashSet<production>(); 
     this.finishes = new HashSet<finish>(); 
     this.productions11 = new HashSet<production>(); 
    } 

    public int Id { get; set; } 
    public string ItemName { get; set; } 
    public string Category { get; set; } 
    public string Status { get; set; } 
    public Nullable<int> minqty { get; set; } 

    public virtual ICollection<sale> sales { get; set; } 

} 

Answer 1

有些事情要提：

（1）SQL工會規則比更輕鬆LINQ。在LINQ（和一般），兩個匿名類型被認爲是相同的，如果所有字段名和型比賽。

（2）SQL中的LINQ工會操作映射如下：

SQL   LINQ 
========= ======= 
UNION  Union 
UNION ALL Concat 

它們應用到你的情況：

var query1 = (from s in lam.sales.AsEnumerable() where s.PartyId == 1 
       select new { s.Date, s.item, s.ReqQty, s.Amount, s.TotalAmount }); 

var query2 = (from q in lam.paydetails where q.partyId == 1 
       select new { q.Date, item = "", ReqQty = "", Amount = "", TotalAmount = q.amount }); 

var queryresult = query1.Concat(query2); 

注意上面確保字段名稱匹配，但你還需要確保類型匹配（因爲我沒有他們，我不能這樣做）。舉例來說，如果s.ReqQty和/或s.Amount都是數字類型，你有null爲可空類型或0（零）更換相應""非可空類型。

UPDATE：根據您的數據模型類，這裏是實際工作查詢：

var query1 = (from s in db.sales where s.PartyId == 1 
       select new { s.Date, s.item, s.ReqQty, s.Amount, TotalAmount = (decimal?)s.TotalAmount }); 

var query2 = (from q in db.paydetails where q.partyId == 1 
       select new { q.Date, item = (item)null, ReqQty = (int?)null, Amount = (int?)null, TotalAmount = q.amount }); 

var queryresult = query1.Concat(query2);