Better SQL for to-one joins

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

@@ -896,7 +896,11 @@ static void UpdateLimit(SelectExpression selectExpression)
                                 innerShaperExpression);
                         }
 
-                        AddJoin(JoinType.OuterApply, ref innerSelectExpression, out _);
+                        // Single-result (to-one) joins never increase result cardinality, so the outer entity's
+                        // identifiers are already sufficient to uniquely identify rows. We don't need to add the
+                        // inner's identifiers to our own; doing so would cause unnecessary reference table JOINs,
+                        // ORDER BY columns, and projections in split collection queries (#29182).
+                        AddJoin(JoinType.OuterApply, ref innerSelectExpression, out _, isToOneJoin: true);
                         var offset = _clientProjections.Count;
                         var count = innerSelectExpression._clientProjections.Count;
 
@@ -3018,7 +3022,8 @@ private void AddJoin(
         JoinType joinType,
         ref SelectExpression innerSelect,
         out bool innerPushdownOccurred,
-        SqlExpression? joinPredicate = null)
+        SqlExpression? joinPredicate = null,
+        bool isToOneJoin = false)
     {
         innerPushdownOccurred = false;
         // Try to convert Apply to normal join
@@ -3099,7 +3104,8 @@ private void AddJoin(
                             joinType == JoinType.CrossApply ? JoinType.InnerJoin : JoinType.LeftJoin,
                             ref innerSelect,
                             out innerPushdownOccurred,
-                            joinPredicate);
+                            joinPredicate,
+                            isToOneJoin);
 
                         return;
                     }
@@ -3153,24 +3159,37 @@ private void AddJoin(
             innerPushdownOccurred = true;
         }
 
+        // If the caller knows this is a to-one join (e.g. SingleResult in ApplyProjection), or if the
+        // join predicate equates all of the inner's identifier columns (PK) to outer columns, then the
+        // join doesn't increase cardinality — the outer identifiers are already sufficient. Skipping the
+        // inner's identifiers avoids unnecessary JOINs, ORDER BY columns, and projections in split
+        // collection queries (#29182).
+        if (!isToOneJoin && joinPredicate is not null && innerSelect._identifier.Count > 0)
+        {
+            isToOneJoin = AllInnerIdentifiersInPredicate(joinPredicate, innerSelect._identifier);
+        }
+
         if (_identifier.Count > 0 && innerSelect._identifier.Count > 0)
         {
-            switch (joinType)
+            if (!isToOneJoin)
             {
-                case JoinType.LeftJoin or JoinType.OuterApply:
-                    _identifier.AddRange(innerSelect._identifier.Select(e => (e.Column.MakeNullable(), e.Comparer)));
-                    break;
+                switch (joinType)
+                {
+                    case JoinType.LeftJoin or JoinType.OuterApply:
+                        _identifier.AddRange(innerSelect._identifier.Select(e => (e.Column.MakeNullable(), e.Comparer)));
+                        break;
 
-                case JoinType.RightJoin:
-                    var nullableOuterIdentifier = _identifier.Select(e => (e.Column.MakeNullable(), e.Comparer)).ToList();
-                    _identifier.Clear();
-                    _identifier.AddRange(nullableOuterIdentifier);
-                    _identifier.AddRange(innerSelect._identifier);
-                    break;
+                    case JoinType.RightJoin:
+                        var nullableOuterIdentifier = _identifier.Select(e => (e.Column.MakeNullable(), e.Comparer)).ToList();
+                        _identifier.Clear();
+                        _identifier.AddRange(nullableOuterIdentifier);
+                        _identifier.AddRange(innerSelect._identifier);
+                        break;
 
-                default:
-                    _identifier.AddRange(innerSelect._identifier);
-                    break;
+                    default:
+                        _identifier.AddRange(innerSelect._identifier);
+                        break;
+                }
             }
         }
         else
@@ -3185,7 +3204,7 @@ private void AddJoin(
         var joinTable = joinType switch
         {
             JoinType.InnerJoin => new InnerJoinExpression(innerTable, joinPredicate!),
-            JoinType.LeftJoin => new LeftJoinExpression(innerTable, joinPredicate!),
+            JoinType.LeftJoin => new LeftJoinExpression(innerTable, joinPredicate!, prunable: isToOneJoin),
             JoinType.RightJoin => new RightJoinExpression(innerTable, joinPredicate!),
             JoinType.CrossJoin => new CrossJoinExpression(innerTable),
             JoinType.CrossApply => new CrossApplyExpression(innerTable),
@@ -3219,6 +3238,57 @@ static void GetPartitions(SelectExpression select, SqlExpression sqlExpression,
             }
         }
 
+        // Checks whether all of the inner select's identifier columns appear as equality terms in the
+        // join predicate. If so, the join is to-one from the outer's perspective (each outer row matches
+        // at most one inner row), meaning the inner identifiers are redundant for row identification.
+        static bool AllInnerIdentifiersInPredicate(
+            SqlExpression joinPredicate,
+            List<(ColumnExpression Column, ValueComparer Comparer)> innerIdentifiers)
+        {
+            Span<bool> matched = innerIdentifiers.Count <= 8
+                ? stackalloc bool[innerIdentifiers.Count]
+                : new bool[innerIdentifiers.Count];
+
+            MatchIdentifiersInPredicate(joinPredicate, innerIdentifiers, matched);
+
+            foreach (var m in matched)
+            {
+                if (!m)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+
+            static void MatchIdentifiersInPredicate(
+                SqlExpression expression,
+                List<(ColumnExpression Column, ValueComparer Comparer)> identifiers,
+                Span<bool> matched)
+            {
+                switch (expression)
+                {
+                    case SqlBinaryExpression { OperatorType: ExpressionType.Equal } binary:
+                        for (var i = 0; i < identifiers.Count; i++)
+                        {
+                            if (!matched[i]
+                                && (identifiers[i].Column.Equals(binary.Left)
+                                    || identifiers[i].Column.Equals(binary.Right)))
+                            {
+                                matched[i] = true;
+                            }
+                        }
+
+                        break;
+
+                    case SqlBinaryExpression { OperatorType: ExpressionType.AndAlso } binary:
+                        MatchIdentifiersInPredicate(binary.Left, identifiers, matched);
+                        MatchIdentifiersInPredicate(binary.Right, identifiers, matched);
+                        break;
+                }
+            }
+        }
+
         static SqlExpression? TryExtractJoinKey(SelectExpression outer, SelectExpression inner, bool allowNonEquality)
         {
             if (inner.Limit != null

test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NonSharedModelBulkUpdatesSqlServerTest.cs

@@ -165,7 +165,6 @@ public override async Task Delete_entity_with_auto_include(bool async)
             """
 DELETE FROM [c]
 FROM [Context30572_Principal] AS [c]
-LEFT JOIN [Context30572_Dependent] AS [c0] ON [c].[DependentId] = [c0].[Id]
 """);
     }
 

test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqlServerTest.cs

@@ -532,18 +532,8 @@ public override async Task Delete_with_LeftJoin(bool async)
 
         AssertSql(
             """
-@p='0'
-@p1='100'
-
 DELETE FROM [o]
 FROM [Order Details] AS [o]
-LEFT JOIN (
-    SELECT [o0].[OrderID]
-    FROM [Orders] AS [o0]
-    WHERE [o0].[OrderID] < 10300
-    ORDER BY [o0].[OrderID]
-    OFFSET @p ROWS FETCH NEXT @p1 ROWS ONLY
-) AS [o1] ON [o].[OrderID] = [o1].[OrderID]
 WHERE [o].[OrderID] < 10276
 """);
     }
@@ -554,18 +544,8 @@ public override async Task Delete_with_LeftJoin_via_flattened_GroupJoin(bool asy
 
         AssertSql(
             """
-@p='0'
-@p1='100'
-
 DELETE FROM [o]
 FROM [Order Details] AS [o]
-LEFT JOIN (
-    SELECT [o0].[OrderID]
-    FROM [Orders] AS [o0]
-    WHERE [o0].[OrderID] < 10300
-    ORDER BY [o0].[OrderID]
-    OFFSET @p ROWS FETCH NEXT @p1 ROWS ONLY
-) AS [o1] ON [o].[OrderID] = [o1].[OrderID]
 WHERE [o].[OrderID] < 10276
 """);
     }

test/EFCore.SqlServer.FunctionalTests/ManyToManyFieldsLoadSqlServerTest.cs

@@ -33,7 +33,7 @@ FROM [JoinOneToTwo] AS [j0]
     WHERE [e1].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneId], [s].[TwoId], [s].[Id], [s0].[OneId], [s0].[TwoId]
+ORDER BY [e].[Id], [s].[OneId], [s].[TwoId], [s0].[OneId]
 """);
     }
 
@@ -59,7 +59,7 @@ FROM [EntityOneEntityTwo] AS [e2]
     WHERE [e3].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[TwoSkipSharedId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s0].[OneSkipSharedId]
 """);
     }
 
@@ -90,7 +90,7 @@ FROM [EntityOneEntityTwo] AS [e4]
     WHERE [e3].[Id] = @p
 ) AS [s1] ON [s].[Id] = [s1].[TwoSkipSharedId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId0], [s1].[TwoSkipSharedId0]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[OneSkipSharedId0]
 """);
     }
 
@@ -121,7 +121,7 @@ FROM [JoinTwoToThree] AS [j]
     INNER JOIN [EntityThrees] AS [e4] ON [j].[ThreeId] = [e4].[Id]
 ) AS [s1] ON [s].[Id] = [s1].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s0].[Id], [s1].[ThreeId], [s1].[TwoId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s1].[ThreeId]
 """);
     }
 
@@ -153,7 +153,7 @@ FROM [JoinTwoToThree] AS [j]
     WHERE [e4].[Id] IN (13, 11)
 ) AS [s1] ON [s].[Id] = [s1].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s0].[Id], [s1].[ThreeId], [s1].[TwoId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s1].[ThreeId]
 """);
     }
 
@@ -193,7 +193,7 @@ public override async Task Load_collection_using_Query_with_join(bool async)
             """
 @p='3'
 
-SELECT [s].[Id], [s].[CollectionInverseId], [s].[Name], [s].[ReferenceInverseId], [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[Id0], [s2].[OneSkipSharedId], [s2].[TwoSkipSharedId], [s2].[Id], [s2].[Name], [s1].[CollectionInverseId], [s1].[Name0], [s1].[ReferenceInverseId]
+SELECT [s].[Id], [s].[CollectionInverseId], [s].[Name], [s].[ReferenceInverseId], [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s2].[OneSkipSharedId], [s2].[TwoSkipSharedId], [s2].[Id], [s2].[Name], [s1].[Id0], [s1].[CollectionInverseId], [s1].[Name0], [s1].[ReferenceInverseId]
 FROM [EntityOnes] AS [e]
 INNER JOIN (
     SELECT [e1].[Id], [e1].[CollectionInverseId], [e1].[Name], [e1].[ReferenceInverseId], [e0].[OneSkipSharedId], [e0].[TwoSkipSharedId]
@@ -216,7 +216,7 @@ FROM [EntityOneEntityTwo] AS [e5]
     WHERE [e6].[Id] = @p
 ) AS [s2] ON [s].[Id] = [s2].[TwoSkipSharedId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[Id0], [s2].[OneSkipSharedId], [s2].[TwoSkipSharedId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s2].[OneSkipSharedId]
 """);
     }
 

test/EFCore.SqlServer.FunctionalTests/ManyToManyLoadSqlServerTest.cs

@@ -33,7 +33,7 @@ FROM [JoinOneToTwo] AS [j0]
     WHERE [e1].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneId], [s].[TwoId], [s].[Id], [s0].[OneId], [s0].[TwoId]
+ORDER BY [e].[Id], [s].[OneId], [s].[TwoId], [s0].[OneId]
 """
                 : """
 @p='3'
@@ -52,7 +52,7 @@ FROM [JoinOneToTwo] AS [j0]
     WHERE [e1].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneId], [s].[TwoId], [s].[Id], [s0].[OneId], [s0].[TwoId]
+ORDER BY [e].[Id], [s].[OneId], [s].[TwoId], [s0].[OneId]
 """);
     }
 
@@ -78,7 +78,7 @@ FROM [EntityOneEntityTwo] AS [e2]
     WHERE [e3].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[TwoSkipSharedId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s0].[OneSkipSharedId]
 """);
     }
 
@@ -109,7 +109,7 @@ FROM [EntityOneEntityTwo] AS [e4]
     WHERE [e3].[Id] = @p
 ) AS [s1] ON [s].[Id] = [s1].[TwoSkipSharedId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId0], [s1].[TwoSkipSharedId0]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[OneSkipSharedId0]
 """);
     }
 
@@ -140,7 +140,7 @@ FROM [JoinTwoToThree] AS [j]
     INNER JOIN [EntityThrees] AS [e4] ON [j].[ThreeId] = [e4].[Id]
 ) AS [s1] ON [s].[Id] = [s1].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s0].[Id], [s1].[ThreeId], [s1].[TwoId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s1].[ThreeId]
 """);
     }
 
@@ -172,7 +172,7 @@ FROM [JoinTwoToThree] AS [j]
     WHERE [e4].[Id] IN (13, 11)
 ) AS [s1] ON [s].[Id] = [s1].[TwoId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s0].[Id], [s1].[ThreeId], [s1].[TwoId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s0].[OneSkipSharedId], [s0].[TwoSkipSharedId], [s1].[ThreeId]
 """);
     }
 
@@ -212,7 +212,7 @@ public override async Task Load_collection_using_Query_with_join(bool async)
             """
 @p='3'
 
-SELECT [s].[Id], [s].[CollectionInverseId], [s].[ExtraId], [s].[Name], [s].[ReferenceInverseId], [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[Id0], [s2].[OneSkipSharedId], [s2].[TwoSkipSharedId], [s2].[Id], [s2].[Name], [s1].[CollectionInverseId], [s1].[ExtraId], [s1].[Name0], [s1].[ReferenceInverseId]
+SELECT [s].[Id], [s].[CollectionInverseId], [s].[ExtraId], [s].[Name], [s].[ReferenceInverseId], [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s2].[OneSkipSharedId], [s2].[TwoSkipSharedId], [s2].[Id], [s2].[Name], [s1].[Id0], [s1].[CollectionInverseId], [s1].[ExtraId], [s1].[Name0], [s1].[ReferenceInverseId]
 FROM [EntityOnes] AS [e]
 INNER JOIN (
     SELECT [e1].[Id], [e1].[CollectionInverseId], [e1].[ExtraId], [e1].[Name], [e1].[ReferenceInverseId], [e0].[OneSkipSharedId], [e0].[TwoSkipSharedId]
@@ -235,7 +235,7 @@ FROM [EntityOneEntityTwo] AS [e5]
     WHERE [e6].[Id] = @p
 ) AS [s2] ON [s].[Id] = [s2].[TwoSkipSharedId]
 WHERE [e].[Id] = @p
-ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s].[Id], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s1].[Id0], [s2].[OneSkipSharedId], [s2].[TwoSkipSharedId]
+ORDER BY [e].[Id], [s].[OneSkipSharedId], [s].[TwoSkipSharedId], [s1].[Id], [s1].[OneSkipSharedId], [s1].[TwoSkipSharedId], [s2].[OneSkipSharedId]
 """);
     }
 

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

@@ -67,7 +67,7 @@ FROM [ManyMN_DB] AS [m2]
     WHERE [m3].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[ManyN_Id]
 WHERE [m].[Id] = @p
-ORDER BY [m].[Id], [s].[Id0], [s].[Id], [s0].[Id]
+ORDER BY [m].[Id], [s].[Id0]
 """,
             //
             """
@@ -95,7 +95,7 @@ FROM [ManyMN_DB] AS [m2]
     WHERE [m3].[Id] = @p
 ) AS [s0] ON [s].[Id] = [s0].[ManyM_Id]
 WHERE [m].[Id] = @p
-ORDER BY [m].[Id], [s].[Id0], [s].[Id], [s0].[Id]
+ORDER BY [m].[Id], [s].[Id0]
 """);
     }
 }