Chapter XIII: Packet Data

@author: Tobin
@date: 2019/10/28 22:32:57

Watch GROUP BY and HAVING clauses

# 创建分组
SELECT vend_id , COUNT(*) AS num_prods
FROM products
GROUP BY vend_id;
#SELECT中，除了聚集语句之外，每个列都需要在GROUP BY语句中给出。
# GROUP BY 位于WHERE语句之后，ORDER BY语句之前。

# HAVING过滤分组，WHERE过滤行
SELECT vend_id , COUNT(*) AS num_prods
FROM products
GROUP BY vend_id
HAVING COUNT(*)>=2;

SELECT vend_id , COUNT(*) AS num_prods
FROM products
WHERE prod_price >=10
GROUP BY vend_id
HAVING COUNT(*)>=2;

# 使用ORDER BY 排序
SELECT order_num, SUM(quantity*item_price) AS ordertotal
FROM orderitems
GROUP BY order_num
HAVING SUM(quantity*item_price) >=50
ORDER BY ordertotal;