diff --git a/lib/features/workspace/table_view_staging.dart b/lib/features/workspace/table_view_staging.dart
index 5fbee04..7c019ab 100644
--- a/lib/features/workspace/table_view_staging.dart
+++ b/lib/features/workspace/table_view_staging.dart
@@ -163,9 +163,20 @@ Future<bool?> showDiscardTableEditsDialog({
   );
 }
 
-/// Throws if a DML statement matched no rows (stale PK / concurrent delete).
+/// Throws unless a staged single-row DML statement matched exactly one row.
+///
+/// 0 rows means a stale key or concurrent delete; 2+ rows means an unkeyed
+/// table has duplicates and the statement would silently rewrite all of them.
+/// Callers run statements in a transaction, so throwing rolls the batch back.
 void expectDmlMatchedRows(int affectedRows) {
-  if (affectedRows >= 1) return;
+  if (affectedRows == 1) return;
+  if (affectedRows > 1) {
+    throw StateError(
+      'Save failed: a statement matched $affectedRows rows instead of 1. '
+      'The table has duplicate rows or no unique key. '
+      'No changes were applied.',
+    );
+  }
   throw StateError(
     'Save failed: a statement matched 0 rows. '
     'The row may have been changed or deleted. Refresh and try again.',
diff --git a/test/core/database/sqlite_connection_test.dart b/test/core/database/sqlite_connection_test.dart
index 0d08e6e..5f75805 100644
--- a/test/core/database/sqlite_connection_test.dart
+++ b/test/core/database/sqlite_connection_test.dart
@@ -432,6 +432,51 @@ void main() {
       expect(rows.first['name'], 'keep');
     });
 
+    test('duplicate-row UPDATE without a key rolls back instead of succeeding',
+        () async {
+      await conn.connect();
+      await conn.execute('CREATE TABLE t (name TEXT)');
+      await conn.execute("INSERT INTO t (name) VALUES ('dup'), ('dup')");
+
+      await expectLater(
+        conn.runInTransaction(() async {
+          expectDmlMatchedRows(
+            await conn.executeAffected(
+              "UPDATE t SET name = 'changed' WHERE name = 'dup'",
+            ),
+          );
+        }),
+        throwsA(
+          isA<StateError>().having(
+            (e) => e.message,
+            'message',
+            contains('matched 2 rows instead of 1'),
+          ),
+        ),
+      );
+
+      final rows = await conn.execute('SELECT name FROM t');
+      expect(rows.map((r) => r['name']), ['dup', 'dup']);
+    });
+
+    test('rowid-addressed UPDATE touches only one of the duplicate rows',
+        () async {
+      await conn.connect();
+      await conn.execute('CREATE TABLE t (name TEXT)');
+      await conn.execute("INSERT INTO t (name) VALUES ('dup'), ('dup')");
+
+      await conn.runInTransaction(() async {
+        expectDmlMatchedRows(
+          await conn.executeAffected(
+            "UPDATE t SET name = 'changed' WHERE \"rowid\" = 1",
+          ),
+        );
+      });
+
+      final rows = await conn.execute('SELECT name FROM t ORDER BY rowid');
+      expect(rows.map((r) => r['name']), ['changed', 'dup']);
+    });
+
     test('handles quotes in quoteIdentifier helper', () {
       expect(
           SqliteConnection.quoteIdentifier('normal_table'), '"normal_table"');
diff --git a/test/core/database/table_mutation_engine_test.dart b/test/core/database/table_mutation_engine_test.dart
index ef9efbc..99a6c2a 100644
--- a/test/core/database/table_mutation_engine_test.dart
+++ b/test/core/database/table_mutation_engine_test.dart
@@ -93,6 +93,32 @@ void main() {
       expect(tx.endsWith('COMMIT;\n'), isTrue);
     });
 
+    test('addresses unkeyed SQLite rows by implicit rowid in UPDATE and DELETE',
+        () {
+      final plan = TableMutationEngine.generatePlan(
+        dialect: SqlDialect.sqlite,
+        tableName: 'notes',
+        columns: const ['rowid', 'body'],
+        primaryKeys: ['rowid'],
+        originalRows: const [
+          ['7', 'dup'],
+          ['8', 'dup'],
+        ],
+        modifiedCells: {
+          0: {1: 'edited'},
+        },
+        insertedRows: [],
+        deletedRowIndices: {1},
+      );
+
+      expect(plan.statementCount, 2);
+      expect(
+        plan.statements[0].sql,
+        'UPDATE "notes" SET "body" = \'edited\' WHERE "rowid" = 7',
+      );
+      expect(plan.statements[1].sql, 'DELETE FROM "notes" WHERE "rowid" = 8');
+    });
+
     test('generates UPDATE statement for MySQL dialect with backticks', () {
       final plan = TableMutationEngine.generatePlan(
         dialect: SqlDialect.mysql,
diff --git a/test/features/extensions/extension_table_view_test.dart b/test/features/extensions/extension_table_view_test.dart
index 611cf64..aac3799 100644
--- a/test/features/extensions/extension_table_view_test.dart
+++ b/test/features/extensions/extension_table_view_test.dart
@@ -107,7 +107,7 @@ void main() {
       expect(mutations[2]['where'], {'id': '2'});
     });
 
-    test('Extension driver mutation response validation requires integer affectedRows >= 1', () {
+    test('Extension driver mutation response validation requires integer affectedRows == 1', () {
       // 1. Missing affectedRows count
       void validateResponse(dynamic res) {
         if (res is! Map) throw StateError('Response is not map');
@@ -147,8 +147,18 @@ void main() {
         )),
       );
 
-      // 4. Positive affectedRows succeeds
-      expect(() => validateResponse({'affectedRows': 3}), returnsNormally);
+      // 4. Multiple matched rows would silently rewrite duplicates
+      expect(
+        () => validateResponse({'affectedRows': 3}),
+        throwsA(isA<StateError>().having(
+          (e) => e.message,
+          'message',
+          contains('matched 3 rows instead of 1'),
+        )),
+      );
+
+      // 5. Exactly one affected row succeeds
+      expect(() => validateResponse({'affectedRows': 1}), returnsNormally);
     });
 
     test('Schema fetch failure is captured as unavailable and disables staging', () async {
diff --git a/test/features/workspace/table_view_staging_test.dart b/test/features/workspace/table_view_staging_test.dart
index 1f23a16..900ed81 100644
--- a/test/features/workspace/table_view_staging_test.dart
+++ b/test/features/workspace/table_view_staging_test.dart
@@ -385,9 +385,21 @@ void main() {
   });
 
   group('expectDmlMatchedRows', () {
-    test('allows 1+ affected rows', () {
+    test('allows exactly 1 affected row', () {
       expect(() => expectDmlMatchedRows(1), returnsNormally);
-      expect(() => expectDmlMatchedRows(3), returnsNormally);
+    });
+
+    test('throws when a statement matched multiple rows', () {
+      expect(
+        () => expectDmlMatchedRows(3),
+        throwsA(
+          isA<StateError>().having(
+            (e) => e.message,
+            'message',
+            contains('matched 3 rows instead of 1'),
+          ),
+        ),
+      );
     });
 
     test('throws on 0-row DML so Save is a failure', () {