SQL使用案例來轉換數據類型

Question

我想總結所有支付的總金額，當我這樣做時答案以科學記數法給出，而不是具有特定小數位數的浮點數。我所關注的專欄是total_amount，如果您可以請告訴我這樣做的正確方法，以及關於Case功能的一些背景，那將非常棒。

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()不改變數據類型，只是值。相反，投後做sum()：你正在使用的數據庫

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;