题目内容：
有订单表orders，包含用户信息userid, 产品信息 productid, 以下( )语句能够返回至少被订购过两回的productid?
A．select productid from orders where count(productid)>1 B．select productid from orders where max(productid)>1
C．select productid from orders where having count(productid)>1 group by productid
D．select productid from orders group by productid having count(productid)>1
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答案解析：