如何为这些表创建SQL请求/命令？

Question

正在寻找连接两个表的SQL行，但在

上填充它

Answer 1

a）每位客户的订单数量。

SELECT C.NAME, COUNT(O.id)
FROM Customers C
INNER JOIN Orders O ON O.customer_id = C.ID
GROUP BY C.NAME

b）拥有三个或更多订单的所有客户的清单。

SELECT C.NAME, COUNT(O.id)
FROM Customers C
INNER JOIN Orders O ON O.customer_id = C.ID
GROUP BY C.NAME
HAVING COUNT(O.id) > 3

c）订购名为“测试项目”的项目的所有客户的清单。

SELECT C.NAME, COUNT(O.id)
FROM Customers C
INNER JOIN Orders O ON O.customer_id = C.ID
WHERE O.item_name = 'test item'
GROUP BY C.NAME

d）未订购名为“测试项目”的项目的所有客户的清单。

SELECT C.NAME, COUNT(O.id)
FROM Customers C
INNER JOIN Orders O ON O.customer_id = C.ID
WHERE O.item_name <> 'test item'
GROUP BY C.NAME