按月和年组mysql查询

Question

按照customer_gender，商店，月份和年份查找2012年之前产品'Beta600'的所有帐户借记卡总额

我运行此查询但我无法得到我想要的结果：

SELECT customer_gender, product_code, month(transactions.trn_date),
year(transactions.trn_date), COUNT(trn_amount)
FROM customers, products, transactions, accounts
WHERE customer.customerid = accounts.customer_id 
AND transactions.account_id = accounts.account_id
AND accounts.product_code = products.product_code AND products.poduct_name = 'Beta600'
AND transactions.trn_date < '1/1/2012' AND accounts.account_currency = 'EUR'
GROUP BY customer_gender, product_code, month(transactions.trn_date),
year(transactions.trn_date)