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串連兩個序列

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使用 Concat 運算子可串連兩個序列。

Concat 運算子是針對已排序的多重集 (Multiset) 所定義，其中接收者和引數的順序相同。

產生結果前的最後一個步驟就是在 SQL 中進行排序。 基於這個理由，會使用 Concat 實作 UNION ALL 運算子，但不保留其引數的順序。 若要確保結果的排序正確無誤，請務必明確地將結果排序。

範例 1

這個範例會使用 Concat 傳回所有 Customer 和 Employee 電話及傳真號碼的序列。

IQueryable<String> custQuery =
    (from cust in db.Customers
    select cust.Phone)
    .Concat
    (from cust in db.Customers
    select cust.Fax)
    .Concat
    (from emp in db.Employees
    select emp.HomePhone)
;

foreach (var custData in custQuery)
{
    Console.WriteLine(custData);
}


Dim custQuery = _
    (From c In db.Customers _
     Select c.Phone) _
    .Concat _
    (From c In db.Customers _
     Select c.Fax) _
    .Concat _
    (From e In db.Employees _
     Select e.HomePhone)

For Each custData In custQuery
    Console.WriteLine(custData)
Next

範例 2

這個範例會使用 Concat 傳回所有 Customer 和 Employee 姓名及電話號碼對應的序列。

var infoQuery =
    (from cust in db.Customers
    select new { Name = cust.CompanyName, cust.Phone }
    )
   .Concat
       (from emp in db.Employees
       select new
       {
           Name = emp.FirstName + " " + emp.LastName,
           Phone = emp.HomePhone
       }
       );

foreach (var infoData in infoQuery)
{
    Console.WriteLine("Name = {0}, Phone = {1}",
        infoData.Name, infoData.Phone);
}

Dim infoQuery = _
    (From cust In db.Customers _
     Select Name = cust.CompanyName, Phone = cust.Phone) _
    .Concat _
        (From emp In db.Employees _
         Select Name = emp.FirstName & " " & emp.LastName, _
             Phone = emp.HomePhone)

For Each infoData In infoQuery
    Console.WriteLine("Name = " & infoData.Name & _
        ", Phone = " & infoData.Phone)
Next

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