--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/UnitTests/Linq/UserTests/GroupBySubqueryTest.cs	Thu Mar 27 21:46:09 2014 +0400
@@ -0,0 +1,104 @@
+using System;
+using System.Linq;
+
+using BLToolkit.Mapping;
+
+using NUnit.Framework;
+
+namespace Data.Linq.UserTests
+{
+	[TestFixture]
+	public class GroupBySubqueryTest : TestBase
+	{
+		class Table1
+		{
+			public long Field1 { get; set; }
+			public int  Field2 { get; set; }
+
+			[Nullable]
+			public int? Field3 { get; set; }
+
+			[Association(ThisKey = "Field1", OtherKey = "Field1", CanBeNull = false)]
+			public Table3 Ref1 { get; set; }
+
+			[Association(ThisKey = "Field3", OtherKey = "Field3", CanBeNull = true)]
+			public Table5 Ref2 { get; set; }
+
+			[Association(ThisKey = "Field2", OtherKey = "Field2", CanBeNull = true)]
+			public Table2 Ref3 { get; set; }
+		}
+
+		class Table2
+		{
+			public int    Field2 { get; set; }
+			public string Field4 { get; set; }
+		}
+
+		class Table3
+		{
+			public int  Field5 { get; set; }
+			public long Field1 { get; set; }
+
+			[AssociationAttribute(ThisKey = "Field5", OtherKey = "Field5", CanBeNull = false)]
+			public Table4 Ref4 { get; set; }
+		}
+
+		class Table4
+		{
+			public int Field5 { get; set; }
+			public int Field6 { get; set; }
+		}
+
+		public class Table5
+		{
+			[Nullable]
+			public int? Field3 { get; set; }
+			public int  Field7 { get; set; }
+
+			[Association(ThisKey = "Field7", OtherKey = "Field7", CanBeNull = true)]
+			public Table6 Ref5 { get; set; }
+		}
+
+		public class Table6
+		{
+			public int    Field7 { get; set; }
+			public string Field8 { get; set; }
+		}
+
+		[Test]
+		public void Test()
+		{
+			using (var db = new TestDbManager())
+			{
+				var q = (
+					from t1 in db.GetTable<Table1>()
+					where t1.Field3 != null
+					select new
+					{
+						t1.Ref1.Ref4.Field6, t1.Ref3.Field4,
+						Field1 = t1.Ref2.Ref5.Field8 ?? string.Empty
+					}
+				).Distinct();
+
+				var sql1 = q.ToString();
+
+				var q2 =
+					from t3 in q
+					group t3 by new { t3.Field6, t3.Field4 }
+					into g
+					where g.Count() > 1
+					select new { g.Key.Field6, EngineeringCircuitNumber = g.Key.Field4, Count = g.Count() };
+
+				var sql2 = q2.ToString();
+
+				var idx = sql2.IndexOf("DISTINCT");
+
+				Assert.That(idx, Is.GreaterThanOrEqualTo(0));
+
+				idx = sql2.IndexOf("Field8", idx);
+
+				Assert.That(idx, Is.GreaterThanOrEqualTo(0));
+			}
+		}
+	}
+}