fix(mysql): fallback to pymysql when MySQLdb is not installed in get_datatype() (#39729)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit_tests/db_engine_specs/test_mysql.py

@@ -15,8 +15,10 @@
 # specific language governing permissions and limitations
 # under the License.
 
+import builtins
 from datetime import datetime
 from decimal import Decimal
+from types import ModuleType
 from typing import Any, Optional
 from unittest.mock import Mock, patch
 
@@ -262,3 +264,42 @@ def test_column_type_mutator(
     mock_cursor.description = description
 
     assert spec.fetch_data(mock_cursor) == expected_result
+
+
+def test_get_datatype_pymysql_fallback():
+    """get_datatype() falls back to pymysql when MySQLdb is not installed."""
+    from superset.db_engine_specs.mysql import MySQLEngineSpec
+
+    # Reset cached type_code_map so the import path is exercised
+    original_type_code_map = MySQLEngineSpec.type_code_map
+    MySQLEngineSpec.type_code_map = {}
+
+    try:
+        # Build a fake pymysql module with constants.FIELD_TYPE
+        fake_field_type = ModuleType("pymysql.constants.FIELD_TYPE")
+        fake_field_type.TINY = 1
+        fake_field_type.VARCHAR = 15
+
+        fake_constants = ModuleType("pymysql.constants")
+        fake_constants.FIELD_TYPE = fake_field_type
+
+        fake_pymysql = ModuleType("pymysql")
+        fake_pymysql.constants = fake_constants
+
+        original_import = builtins.__import__
+
+        def mock_import(name: str, *args: Any, **kwargs: Any) -> Any:
+            if name == "MySQLdb":
+                raise ImportError("No module named 'MySQLdb'")
+            if name == "pymysql":
+                return fake_pymysql
+            return original_import(name, *args, **kwargs)
+
+        with patch("builtins.__import__", side_effect=mock_import):
+            assert MySQLEngineSpec.get_datatype(1) == "TINY"
+            assert MySQLEngineSpec.get_datatype(15) == "VARCHAR"
+            assert MySQLEngineSpec.get_datatype("BIGINT") == "BIGINT"
+            assert MySQLEngineSpec.get_datatype(999) is None
+    finally:
+        # Restore original state
+        MySQLEngineSpec.type_code_map = original_type_code_map