[release/6.0] Query: Don't add grouping key to projection when Distinct is applied

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.cs

@@ -2996,7 +2996,10 @@ private SqlRemappingVisitor PushdownIntoSubqueryInternal()
                 }
             }
 
-            if (subquery._groupBy.Count > 0)
+            if (subquery._groupBy.Count > 0
+                && (AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue28039", out var enabled28039)
+                    && enabled28039
+                    || !subquery.IsDistinct))
             {
                 foreach (var key in subquery._groupBy)
                 {

test/EFCore.Specification.Tests/Query/NorthwindGroupByQueryTestBase.cs

@@ -2027,6 +2027,23 @@ from g in grouping
                 entryCount: 63);
         }
 
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task Join_GroupBy_Aggregate_distinct_single_join(bool async)
+        {
+            return AssertQuery(
+                async,
+                ss =>
+                    from c in ss.Set<Customer>()
+                    join a in ss.Set<Order>().GroupBy(o => new { o.CustomerID, o.OrderDate.Value.Year })
+                            .Where(g => g.Count() > 5)
+                            .Select(g => new { CustomerID = g.Key.CustomerID, LastOrderID = g.Max(o => o.OrderID) })
+                            .Distinct()
+                        on c.CustomerID equals a.CustomerID
+                    select new { c, a.LastOrderID },
+                entryCount: 31);
+        }
+
         [ConditionalTheory]
         [MemberData(nameof(IsAsyncData))]
         public virtual Task Join_GroupBy_Aggregate_with_left_join(bool async)

test/EFCore.Specification.Tests/Query/SimpleQueryTestBase.cs

@@ -986,5 +986,69 @@ protected class Child26744
             public DateTime? SomeOtherNullableDateTime { get; set; }
             public Parent26744 Parent { get; set; }
         }
+
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual async Task Pushdown_does_not_add_grouping_key_to_projection_when_distinct_is_applied(bool async)
+        {
+            var contextFactory = await InitializeAsync<Context28039>();
+            using var db = contextFactory.CreateContext();
+
+
+            var queryResults = (from i in db.IndexData.Where(a => a.Parcel == "some condition")
+                                            .Select(a => new SearchResult { ParcelNumber = a.Parcel, RowId = a.RowId })
+                                group i by new { i.ParcelNumber, i.RowId } into grp
+                                where grp.Count() == 1
+                                select grp.Key.ParcelNumber).Distinct();
+
+            var jsonLookup = (from dcv in db.TableData.Where(a => a.TableId == 123)
+                              join wos in queryResults
+                              on dcv.ParcelNumber equals wos
+                              orderby dcv.ParcelNumber
+                              select dcv.JSON).Take(123456);
+
+
+            var result = async
+                ? await jsonLookup.ToListAsync()
+                : jsonLookup.ToList();
+        }
+
+        protected class Context28039 : DbContext
+        {
+            public Context28039(DbContextOptions options)
+                : base(options)
+            {
+            }
+
+            public DbSet<IndexData> IndexData { get; set; }
+            public DbSet<TableData> TableData { get; set; }
+        }
+
+        public class TableData : EntityBase
+        {
+            public int TableId { get; set; }
+            public string ParcelNumber { get; set; }
+            public short RowId { get; set; }
+            public string JSON { get; set; }
+
+        }
+
+        public abstract class EntityBase
+        {
+            [Key]
+            public int ID { get; set; }
+        }
+        public class IndexData : EntityBase
+        {
+            public string Parcel { get; set; }
+            public int RowId { get; set; }
+        }
+
+        internal class SearchResult
+        {
+            public string ParcelNumber { get; set; }
+            public int RowId { get; set; }
+            public string DistinctValue { get; set; }
+        }
     }
 }

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindGroupByQuerySqlServerTest.cs

@@ -1517,6 +1517,21 @@ HAVING COUNT(*) > 5
 INNER JOIN [Orders] AS [o0] ON [c].[CustomerID] = [o0].[CustomerID]");
         }
 
+        public override async Task Join_GroupBy_Aggregate_distinct_single_join(bool async)
+        {
+            await base.Join_GroupBy_Aggregate_distinct_single_join(async);
+
+            AssertSql(
+                @"SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region], [t].[LastOrderID]
+FROM [Customers] AS [c]
+INNER JOIN (
+    SELECT DISTINCT [o].[CustomerID], MAX([o].[OrderID]) AS [LastOrderID]
+    FROM [Orders] AS [o]
+    GROUP BY [o].[CustomerID], DATEPART(year, [o].[OrderDate])
+    HAVING COUNT(*) > 5
+) AS [t] ON [c].[CustomerID] = [t].[CustomerID]");
+        }
+
         public override async Task Join_GroupBy_Aggregate_with_left_join(bool async)
         {
             await base.Join_GroupBy_Aggregate_with_left_join(async);

test/EFCore.SqlServer.FunctionalTests/Query/SimpleQuerySqlServerTest.cs

@@ -297,5 +297,25 @@ WHERE [c].[SomeNullableDateTime] IS NULL
 ) AS [t0] ON [p].[Id] = [t0].[ParentId]
 WHERE [t0].[SomeOtherNullableDateTime] IS NOT NULL");
         }
+
+        public override async Task Pushdown_does_not_add_grouping_key_to_projection_when_distinct_is_applied(bool async)
+        {
+            await base.Pushdown_does_not_add_grouping_key_to_projection_when_distinct_is_applied(async);
+
+            AssertSql(
+                @"@__p_0='123456'
+
+SELECT TOP(@__p_0) [t].[JSON]
+FROM [TableData] AS [t]
+INNER JOIN (
+    SELECT DISTINCT [i].[Parcel]
+    FROM [IndexData] AS [i]
+    WHERE [i].[Parcel] = N'some condition'
+    GROUP BY [i].[Parcel], [i].[RowId]
+    HAVING COUNT(*) = 1
+) AS [t0] ON [t].[ParcelNumber] = [t0].[Parcel]
+WHERE [t].[TableId] = 123
+ORDER BY [t].[ParcelNumber]");
+        }
     }
 }