SQL基础教程（第2版）第3章 聚合与排序：练习题

product_name VARCHAR数据类型不支持 聚合函数SUM 求和算数运算；

SELECT子句 后面只能存在 GROUP BY子句中指定的列名（也就是聚合键）；

子句的书写顺序 ，1. SELECT → 2. FROM → 3. WHERE → 4. GROUP BY

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SELECT product_type, SUM(sale_price), SUM(purchase_price)
  FROM Product
 GROUP BY product_type
HAVING SUM(sale_price) > SUM(purchase_price) * 1.5;

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SELECT *
  FROM Product
 ORDER BY regist_date DESC, sale_price;

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