SQL question

Note: Google bigquery - handy-bonbon - order_entry_dataset(free, public)

Question:

Which month (be sure to say from which year) had thelargest percentage decrease in sales over the prior month? Justifyyour rationale and show your SQL query (Hint: use the LAGfunction).

This is my code and I don't know how to fix it.

SELECT

FORMAT_DATE("%Y-%m", order_date) ASOrder_month,

ROUND(SUM(unit_price * quantity), 2) ASAmount_Ordered,

LAG(ROUND( SUM(unit_price * quantity), 2),1,0) OVER(ORDER BY FORMAT_DATE("%Y-%m", order_date)) ASLast_Row

FROM`handy-bonbon-142723.order_entry_dataset.customers_table`

INNER JOIN

`handy-bonbon-142723.order_entry_dataset.orders_table`USING (customer_id)

INNER JOIN

`handy-bonbon-142723.order_entry_dataset.order_items_table`USING(order_id)

INNER JOIN

`handy-bonbon-142723.order_entry_dataset.products_table`USING(PRODUCT_ID)

GROUP BY ORDER_DATE

;