app.py

@@ -951,9 +951,11 @@ def save_pdf_as_webp(file, path):
 
 
 def get_active_months_query(visible_lists_query=None):
-    if db.engine.name == "sqlite":
+    if db.engine.name in ("sqlite",):
         month_col = func.strftime("%Y-%m", ShoppingList.created_at)
-    else:
+    elif db.engine.name in ("mysql", "mariadb"):
+        month_col = func.date_format(ShoppingList.created_at, "%Y-%m")
+    else:  # PostgreSQL i inne wspierające to_char
         month_col = func.to_char(ShoppingList.created_at, "YYYY-MM")
 
     query = db.session.query(month_col.label("month"))