Question

当我这样做一个查询时：

SELECT payment.customer_id, COUNT(payment.customer_id), SUM(payment.amount)
FROM payment 
GROUP BY customer_id
ORDER BY SUM(payment.amount) DESC
LIMIT 10

它完美无缺，但是当我尝试从另一个表中加入一个字段时，它会失败：

SELECT payment.customer_id, customer.email COUNT(payment.customer_id), SUM(payment.amount)
FROM payment 
GROUP BY customer_id
ORDER BY SUM(payment.amount) DESC
LIMIT 10
JOIN customer
ON payment.customer_id = customer.customer_id

我做错了什么？如何从客户表中添加电子邮件列？

Answer 1

要加入，您必须在From关键字之后使用它，如下面的

Select Table1.customer_id,Table1.email,Table1.amt from (
SELECT payment.customer_id, customer.email COUNT(payment.customer_id) email, SUM(payment.amount) amt
FROM payment 
GROUP BY customer_id
ORDER BY SUM(payment.amount) DESC
LIMIT 10
) Table1 JOIN customer
ON Table1.customer_id = customer.customer_id

Answer 2

你错放了JOIN;它属于FROM子句。您的SELECT条款中也缺少逗号。

SELECT c.customer_id, c.email, COUNT(p.payment_id), SUM(p.amount)
FROM customer c
JOIN payment p ON p.customer_id = c.customer_id
GROUP BY c.customer_id
ORDER BY SUM(p.amount) DESC
LIMIT 10;

看到我在FROM和JOIN中切换了表格。这不是必要的，但在我看来感觉好一点，说：给我的客户他们的付款数据。如果您希望客户没有付款数据，请切换到LEFT JOIN。

在我添加JOIN后，Postgresql查询无法正常工作

2 个答案: