一、分组+过滤+排序

检索总计订单价格大于等于 50 的订单的订单号和总计订单价格

SELECT order_num, SUM(quantity*item_price) AS orderTotal
FROM orderItems
GROUP BY order_num 
HAVING SUM(quantity*item_price) >= 50
ORDER BY orderTotal

• GROUP BY 子句用来按订单号(order_num)分组数据，以便SUM(*)函数能够返回总计订单价格
• HAVING 子句过滤数据，使得只返回总计订单价格大于等于 50 的订单
• ORDER BY 子句排序输出

二、SELECT 子句顺序

image.png
image.png