题解 | #纠错3#

• 先执行GROUP BY order_num，对所有字段按照order_num 分组，
• 再执行HAVING items >= 3，对分组进行过滤，即查询出满足items大于等于3的记录，
• 再执行SELECT order_num, COUNT(order_num) AS items，
• 最后执行ORDER BY items, order_num;对记录进行排序，默认是升序。

SELECT order_num, COUNT(order_num) AS items 
FROM OrderItems 
GROUP BY order_num 
HAVING items >= 3
ORDER BY items, order_num;

附DQL执行顺序