Finish No.4

实验四.md

@@ -36,7 +36,7 @@ SHOW FULL COLUMNS FROM sales;
 SELECT * FROM sales WHERE tot_amt >= 100;
 ```
 
-#### 5. 选取订单金额由高到低排序的前 10% 订单数据
+#### 5. 选取订单金额由高到低排序的前 20% 订单数据
 
 ```mysql
 SHOW FULL COLUMNS FROM sales;
@@ -44,17 +44,51 @@ SHOW FULL COLUMNS FROM sales;
 # 排序从小到大输出可以用 SELECT * from sales ORDER BY tot_amt ASC;
 
 # 看前三条就是 SELECT * from sales ORDER BY tot_amt DESC LIMIT 3;
+# 看随机的 10% 就是 SELECT * from sales WHERE RAND() < 0.1 ORDER BY tot_amt;
+
+SET @sql := CONCAT( 'SELECT * FROM sales ORDER BY tot_amt DESC LIMIT '
+                  , (SELECT ROUND(COUNT(*) * 0.2) FROM sales));
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DROP PREPARE stmt;
+
 ```
 
 #### 6. 查找出职称为经理或职称为会计的女员工的信息
 
+```mysql
+SHOW FULL COLUMNS FROM employee;
+SELECT * FROM employee WHERE emp_sex="女" AND emp_title LIKE "%经理" OR emp_title LIKE "%会计";
+```
+
 #### 7. 删除 sales 表中作废的订单（其发票号码为 34600376）
 
 > 注意约束！
 
+本处，因为 `order_no` 有了外键引用，所以子表为 `sales` 表，父表为 `sale_item` 表，删除先删除子表数据。
+
+```mysql
+SELECT * FROM sales WHERE invoice_no="34600376";
+DELETE FROM sales WHERE order_no="11035462019111100000020957";
+DELETE FROM sale_item WHERE order_no="11035462019111100000020957";
+```
+
 #### 8. 计算出一共销售了几种产品
 
-#### 9. 显示 sale_item 表中每种个别产品的订购金额总和，并且一句销售金额由大到小排列来显示出每一种产品的排行榜
+```mysql
+SELECT COUNT(DISTINCT prod_id) as "共销售产品数" FROM sale_item;
+```
+
+#### 9. 显示 sale_item 表中每种个别产品的订购金额总和，并且依据销售金额由大到小排列来显示出每一种产品的排行榜
+
+```mysql
+SELECT prod_id AS "产品编号", SUM(qty * unit_price) AS "销售总额" FROM sale_item GROUP BY prod_id ORDER BY SUM(qty * unit_price) DESC;
+```
 
 #### 10. 计算每一产品每月的销售金额综合，并将结果按销售月份及产品编号排序
 
+```mysql
+# 仅仅按年月输出总销售金额并按月排序 select YEAR(order_date) AS "年份", MONTH(order_date) AS "月份", SUM(tot_amt) AS "销售总额" FROM sales GROUP BY MONTH(order_Date);
+SELECT prod_id AS "产品编号", MONTH(order_date) AS "月份", SUM(qty * unit_price) AS "销售总额" FROM sale_item GROUP BY prod_id ORDER BY MONTH(order_Date) ASC, prod_id ASC;
+```
+