int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 }; var squaresOfNumbers = from i in numbers join j in numbers on i equals j select (new { aa = i, bb = i * j }); foreach (var kk in squaresOfNumbers) Console.WriteLine(kk.aa.ToString() + " - - " + kk.bb.ToString());

notes: 1) the condition "i equals j" cannot be written as "j equals i" - unlike TSQL 2) new { aa = i, bb = i * j } is an anonymous object 3) Actual execution (for square nXn) did not happen until last line --"var kk in squaresOfNumbers"

========================== Above code makes a cross join where a filter is applied with a condition. Following is a way to make Left outer or right outer join // left outer join -- check ".DefaultIfEmpty()" var squaresOfNumbers2 = from i in numbers join j in numbers on i equals j into tempj from k in tempj from jj in tempj.DefaultIfEmpty() select (new { aa = i, bb = i * jj }); // for Right outer join ".DefaultIfEmpty()" need to applied on first list

// a more decent way of doing cross join is var squaresOfNumbers3 = from i in numbers from j in numbers where i == j select (new { aa = i, bb = i * j });

// simple Join example int?[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 , null}; var combined2 = from d in numbers join h in numbers on 1 equals 1 into dh from subH in dh where d != subH //&& d!= null && subDH !=null select new { aa = d, bb = subH * d };