查询19年所有客户的订单总金额，并按总金额从大到小排序

用SQL语句，查询2019年所有客户的订单总金额，并按总金额从大到小排序。(客户表customer, 订单表orders, 订单明细表orderitem) ？

SELECT sum(i.订单金额) from orderitem i, orders o, customer c
on i.订单Id=o.订单Id and 
on c.客户Id=o.客户Id
where year(i.订单时间)='2019'
GROUP BY  c.客户Id
order BY sum(i.订单金额) desc

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