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Concatenate Two Sequences

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Use the Concat operator to concatenate two sequences.

The Concat operator is defined for ordered multisets where the orders of the receiver and the argument are the same.

Ordering in SQL is the final step before results are produced. For this reason, the Concat operator is implemented by using UNION ALL and does not preserve the order of its arguments. To make sure ordering is correct in the results, make sure to explicitly order the results.

Example 1

This example uses Concat to return a sequence of all Customer and Employee telephone and fax numbers.

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

Example 2

This example uses Concat to return a sequence of all Customer and Employee name and telephone number mappings.

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

See also