Linq to query matching column from a table and populate in another table

Question

I have a table as below:

Id	First Name	Last Name
1	John	Murray
2	Smith	Murray
3	Natasha	Murray
4	Steve	Kay
5	Bill	Kay

Now, If I query for a name example John , it should produce the results with the matching records with same lastname and put into another table as below:

Id	Name	Matching name
1	John	Smith
2	John	Natasha

How can i achieve this using Linq?

Answer 1

Lets define the class for data

class Table
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

this is something that should be part of your question. Now fill in the data

Table[] table = new Table[]
{
    new Table{ Id = 1, FirstName = "John", LastName = "Murray" },
    new Table{ Id = 2, FirstName = "Smith", LastName = "Murray" },
    new Table{ Id = 3, FirstName = "Natasha", LastName = "Murray" },
    new Table{ Id = 4, FirstName = "Steve", LastName = "Kay" },
    new Table{ Id = 5, FirstName = "Bill", LastName = "Kay" }
};

and that is also something that should be part of your question. If you omit that you greatly reduce chance of getting an aswer. Now just join the table with itself on the last name.

var query = from t1 in table
            from t2 in table
            where t1.LastName == t2.LastName && t1.Id != t2.Id
            select new { t2.Id, Name = t1.FirstName, MatchingName = t2.FirstName };

foreach (var row in query.Where(t => t.Name == "John"))
{
    Console.WriteLine(row);
}

and voilà

 { Id = 2, Name = John, MatchingName = Smith }
 { Id = 3, Name = John, MatchingName = Natasha }

The only thing that is different is the Id, from the data provided I have no idea how John or Natasha could be related to Id number 2.