Add regression tests for issue#10012

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

@@ -2205,6 +2205,61 @@ public virtual Task GroupBy_aggregate_over_a_subquery(bool async)
                     }));
         }
 
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task GroupBy_aggregate_join_with_grouping_key(bool async)
+        {
+            return AssertQuery(
+                async,
+                ss => ss.Set<Order>()
+                    .GroupBy(o => o.CustomerID)
+                    .Select(g => new { g.Key, Count = g.Count() })
+                    .Join(ss.Set<Customer>(), o => o.Key, c => c.CustomerID, (o, c) => new { c, o.Count }),
+                elementSorter: a => a.c.CustomerID,
+                elementAsserter: (e, a) =>
+                {
+                    AssertEqual(e.c, a.c);
+                    AssertEqual(e.Count, a.Count);
+                },
+                entryCount: 89);
+        }
+
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task GroupBy_aggregate_join_with_group_result(bool async)
+        {
+            return AssertQuery(
+                async,
+                ss => ss.Set<Order>()
+                    .GroupBy(o => o.CustomerID, e => e.OrderDate)
+                    .Select(g => new { g.Key, LastOrderDate = g.Max() })
+                    .Join(ss.Set<Order>(), o => o, i => new { Key = i.CustomerID, LastOrderDate = i.OrderDate }, (_, x) => x),
+                entryCount: 90);
+        }
+
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task GroupBy_aggregate_from_right_side_of_join(bool async)
+        {
+            return AssertQuery(
+                async,
+                ss => (from c in ss.Set<Customer>()
+                       join o in ss.Set<Order>().GroupBy(i => i.CustomerID).Select(e => new { e.Key, Max = e.Max(i => i.OrderDate) })
+                         on c.CustomerID equals o.Key
+                       select new { c, o.Max })
+                      .OrderBy(e => e.Max)
+                      .ThenBy(c => c.c.CustomerID)
+                      .Skip(10)
+                      .Take(10),
+                assertOrder: true,
+                elementAsserter: (e, a) =>
+                {
+                    AssertEqual(e.c, a.c);
+                    AssertEqual(e.Max, a.Max);
+                },
+                entryCount: 10);
+        }
+
         #endregion
 
         #region GroupByWithoutAggregate

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

@@ -1930,6 +1930,52 @@ FROM [Orders] AS [o]
 GROUP BY [o].[CustomerID]");
         }
 
+        public override async Task GroupBy_aggregate_join_with_grouping_key(bool async)
+        {
+            await base.GroupBy_aggregate_join_with_grouping_key(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].[c] AS [Count]
+FROM (
+    SELECT [o].[CustomerID], COUNT(*) AS [c]
+    FROM [Orders] AS [o]
+    GROUP BY [o].[CustomerID]
+) AS [t]
+INNER JOIN [Customers] AS [c] ON [t].[CustomerID] = [c].[CustomerID]");
+        }
+
+        public override async Task GroupBy_aggregate_join_with_group_result(bool async)
+        {
+            await base.GroupBy_aggregate_join_with_group_result(async);
+
+            AssertSql(
+                @"SELECT [o0].[OrderID], [o0].[CustomerID], [o0].[EmployeeID], [o0].[OrderDate]
+FROM (
+    SELECT [o].[CustomerID], MAX([o].[OrderDate]) AS [c]
+    FROM [Orders] AS [o]
+    GROUP BY [o].[CustomerID]
+) AS [t]
+INNER JOIN [Orders] AS [o0] ON (([t].[CustomerID] = [o0].[CustomerID]) OR ([t].[CustomerID] IS NULL AND [o0].[CustomerID] IS NULL)) AND (([t].[c] = [o0].[OrderDate]) OR ([t].[c] IS NULL AND [o0].[OrderDate] IS NULL))");
+        }
+
+        public override async Task GroupBy_aggregate_from_right_side_of_join(bool async)
+        {
+            await base.GroupBy_aggregate_from_right_side_of_join(async);
+
+            AssertSql(
+                @"@__p_0='10'
+
+SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region], [t].[c] AS [Max]
+FROM [Customers] AS [c]
+INNER JOIN (
+    SELECT [o].[CustomerID], MAX([o].[OrderDate]) AS [c]
+    FROM [Orders] AS [o]
+    GROUP BY [o].[CustomerID]
+) AS [t] ON [c].[CustomerID] = [t].[CustomerID]
+ORDER BY [t].[c], [c].[CustomerID]
+OFFSET @__p_0 ROWS FETCH NEXT @__p_0 ROWS ONLY");
+        }
+
         public override async Task GroupBy_with_grouping_key_using_Like(bool async)
         {
             await base.GroupBy_with_grouping_key_using_Like(async);