小编Jay*_*Jay的帖子

此查询在几分之一秒内执行:

SELECT customers.customers_id, customers_firstname, customers_lastname, customers.customers_email_address, max(date_purchased) 
FROM customers join orders on customers.customers_id = orders.customers_id 
group by customers.customers_id;

如果我将连接更改为左连接,它似乎挂起.我尝试将其限制为10条记录,但仍需要9秒.我究竟做错了什么？

提前致谢.