Question

我目前在我的数据库中有两个表：

“customers”的列：customer_id，customer_name
“付款”的列：payment_id，customer_id，year，paid （bool），付款人

“年”一栏表示“付款人”已付款的年份。

这只给我一个付费专栏：

SELECT customer_id, paid AS paid_for_2017 FROM customers LEFT JOIN payments ON customers.customer_id=payments.customer_id AND year=2017;

现在我需要一个SELECT查询，它给出了以下内容：

customer_name, paid_for_2017, paid_for_2018,...

我该怎么做？我应该更改我的数据库设计吗？欢迎提出建议。

Answer 1

如果你知道这些年份，你可以使用条件聚合：

SELECT customer_id,
       SUM(CASE WHEN year = 2017 THEN paid END) AS paid_for_2017,
       SUM(CASE WHEN year = 2018 THEN paid END) AS paid_for_2018
FROM customers c LEFT JOIN
     payments p
     ON c.customer_id = p.customer_id
GROUP BY customer_id;

年度付款的数据库设计

1 个答案: