Fix SQL vs. Polars backend detection for pydiverse.transform

src/pydiverse/pipedag/backend/table/sql/hooks.py

@@ -940,22 +940,19 @@ def materialize(cls, store, table: Table[pdt.Table], stage_name):
 
         t = table.obj
         table = table.copy_without_obj()
-        try:
-            # detect SQL by checking whether build_query() succeeds
-            query = t >> build_query()
-        except Exception:
+        query = t >> build_query()
+        # detect SQL by checking whether build_query() succeeds
+        if query is not None:
+            # continue with SQL case handling
+            table.obj = sa.text(str(query))
+            hook = store.get_hook_subclass(SQLAlchemyTableHook)
+            return hook.materialize(store, table, stage_name)
+        else:
             # use Polars for dataframe handling
             table.obj = t >> export(Polars())
             hook = store.get_hook_subclass(PolarsTableHook)
             return hook.materialize(store, table, stage_name)
 
-        # continue with SQL case handling
-        table.obj = sa.text(query)
-        hook = store.get_hook_subclass(SQLAlchemyTableHook)
-        return hook.materialize(store, table, stage_name)
-
-        raise NotImplementedError
-
     @classmethod
     def retrieve(
         cls,