I have a custom list named "Custom" which has the following columns.

1.) Title
2.) Test

I need to use CAML query and get only the items which has non nullable values in "Test" column.

Code snippet:

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.SharePoint;
 
namespace ISNOTNULL
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable dtOnsiteInfo = new DataTable();
            using (SPSite site = new SPSite("http://serverName/sites/Vijai"))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    SPList list = web.Lists.TryGetList("Custom");
                    SPQuery query = new SPQuery();
                    query.Query = "<Where><IsNotNull><FieldRef Name='Test' /></IsNotNull></Where>";
                    SPListItemCollection itemColl = list.GetItems(query);
                    foreach (SPListItem item in itemColl)
                    {
                        Console.WriteLine(item["Title"]);
                    }
                    Console.ReadLine();                  
                }
            }
        }
    }
}