SQL使用案例来转换数据类型

Question

我想总结所有支付的总金额，当我这样做时答案以科学记数法给出，而不是具有特定小数位数的浮点数。我所关注的专栏是total_amount，如果您可以请告诉我这样做的正确方法，以及关于Case功能的一些背景，那将非常棒。

Select customer.customer_id, customer.email, count(payment.payment_date) as payments_count, 
round(sum(Cast(payment.amount as numeric(4,2))), 2) as total_amount 
From customer join payment 
on customer.customer_id = payment.customer_id 
group by customer.customer_id 

Answer 1

round()不改变数据类型，只是值。相反，投后做sum()：你正在使用的数据库

Select c.customer_id, c.email, count(p.payment_date) as payments_count, 
     Cast(sum(p.amount) as numeric(4, 2)) as total_amount 
From customer c join 
    payment p 
    on c.customer_id = p.customer_id 
group by c.customer_id;