diff --git a/sqlmesh/core/engine_adapter/mssql.py b/sqlmesh/core/engine_adapter/mssql.py
index 200640f305..60fe99ffc4 100644
--- a/sqlmesh/core/engine_adapter/mssql.py
+++ b/sqlmesh/core/engine_adapter/mssql.py
@@ -212,6 +212,7 @@ def merge(
         if merge_filter:
             on = exp.and_(merge_filter, on)
 
+        match_expressions = []
         if not when_matched:
             match_condition = None
             unique_key_names = [y.name for y in unique_key]
@@ -230,23 +231,24 @@ def merge(
                 )
             )
 
-            match_expressions = [
-                exp.When(
-                    matched=True,
-                    source=False,
-                    condition=match_condition,
-                    then=exp.Update(
-                        expressions=[
-                            exp.column(col, MERGE_TARGET_ALIAS).eq(
-                                exp.column(col, MERGE_SOURCE_ALIAS)
-                            )
-                            for col in columns_to_types_no_keys
-                        ],
-                    ),
+            if target_columns_no_keys:
+                match_expressions.append(
+                    exp.When(
+                        matched=True,
+                        source=False,
+                        condition=match_condition,
+                        then=exp.Update(
+                            expressions=[
+                                exp.column(col, MERGE_TARGET_ALIAS).eq(
+                                    exp.column(col, MERGE_SOURCE_ALIAS)
+                                )
+                                for col in columns_to_types_no_keys
+                            ],
+                        ),
+                    )
                 )
-            ]
         else:
-            match_expressions = when_matched.copy().expressions
+            match_expressions.extend(when_matched.copy().expressions)
 
         match_expressions.append(
             exp.When(
diff --git a/tests/core/engine_adapter/test_mssql.py b/tests/core/engine_adapter/test_mssql.py
index d32343d593..eef0a320da 100644
--- a/tests/core/engine_adapter/test_mssql.py
+++ b/tests/core/engine_adapter/test_mssql.py
@@ -456,6 +456,8 @@ def test_merge_pandas(
     temp_table_mock.return_value = make_temp_table_name(table_name, temp_table_id)
 
     df = pd.DataFrame({"id": [1, 2, 3], "ts": [1, 2, 3], "val": [4, 5, 6]})
+
+    # 1 key
     adapter.merge(
         target_table=table_name,
         source_table=df,
@@ -476,6 +478,7 @@ def test_merge_pandas(
         f"DROP TABLE IF EXISTS [__temp_target_{temp_table_id}];",
     ]
 
+    # 2 keys
     adapter.cursor.reset_mock()
     adapter._connection_pool.get().reset_mock()
     temp_table_mock.return_value = make_temp_table_name(table_name, temp_table_id)
@@ -499,6 +502,29 @@ def test_merge_pandas(
         f"DROP TABLE IF EXISTS [__temp_target_{temp_table_id}];",
     ]
 
+    # all model columns are keys
+    adapter.cursor.reset_mock()
+    adapter._connection_pool.get().reset_mock()
+    temp_table_mock.return_value = make_temp_table_name(table_name, temp_table_id)
+    adapter.merge(
+        target_table=table_name,
+        source_table=df,
+        columns_to_types={
+            "id": exp.DataType.build("int"),
+            "ts": exp.DataType.build("TIMESTAMP"),
+        },
+        unique_key=[exp.to_identifier("id"), exp.to_column("ts")],
+    )
+    adapter._connection_pool.get().bulk_copy.assert_called_with(
+        f"__temp_target_{temp_table_id}", [(1, 1), (2, 2), (3, 3)]
+    )
+
+    assert to_sql_calls(adapter) == [
+        f"""IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = '__temp_target_{temp_table_id}') EXEC('CREATE TABLE [__temp_target_{temp_table_id}] ([id] INTEGER, [ts] DATETIME2)');""",
+        f"MERGE INTO [target] AS [__MERGE_TARGET__] USING (SELECT CAST([id] AS INTEGER) AS [id], CAST([ts] AS DATETIME2) AS [ts] FROM [__temp_target_{temp_table_id}]) AS [__MERGE_SOURCE__] ON [__MERGE_TARGET__].[id] = [__MERGE_SOURCE__].[id] AND [__MERGE_TARGET__].[ts] = [__MERGE_SOURCE__].[ts] WHEN NOT MATCHED THEN INSERT ([id], [ts]) VALUES ([__MERGE_SOURCE__].[id], [__MERGE_SOURCE__].[ts]);",
+        f"DROP TABLE IF EXISTS [__temp_target_{temp_table_id}];",
+    ]
+
 
 def test_replace_query(make_mocked_engine_adapter: t.Callable):
     adapter = make_mocked_engine_adapter(MSSQLEngineAdapter)