using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string item1 = "item1"; // whatever you want

        string item2 = "item2"; // 2nd value whatever you want

        string query = "select ["+  item1 +"], ["+ item2 +"] from [table] where [" + item2 + "] = 'value' and [columnX] = 2"; // query whatever you want

        var queries = new List<string>();

        string[] columns = new string[]

        {

            "columnA",

            "columnB",

            "columnC",

            "columnD",

            "columnE",

            "columnF",

            "columnG",

            "columnH",

            "columnI",

            "columnJ"

        };

        var combinations = new List<Tuple<string,string>>(); //new Dictionary<string, string>();

        // combination

        for(int i=0; i<9; i++)

        {

            for(int j=i+1;j<10; j++)

            {

                combinations.Add(Tuple.Create(columns[i],columns[j]));

                Console.WriteLine(columns[i] +','+ columns[j]);

            }

        }

​

        // replacing

        int count=0;

        foreach(var kvp in combinations)

        {

            string temp = query.Replace(item1, kvp.Item1);

            temp = temp.Replace(item2, kvp.Item2);

            queries.Add(temp);

            Console.WriteLine(temp);

            count++;

        }

        //number of combi

        Console.WriteLine(count);

    }

}