SQL笔记(精简版)
文章目录
-
- 数据库结构图
- 1. 检索数据
-
- 1.1 选择数据库
- 1.2 选择单列
- 1.3 选择多列
- 1.4 选择所有列
- 1.5 检索不同的值
- 1.6 限制结果
- 1.7 注释
- 第一章练习题
- 2. 排序检索数据
-
- 2.1 排序数据
- 2.2 按多个列排序
- 2.3 按排列位置排序
- 2.4 指定排序方向
- 第二章练习题
- 3. 过滤数据
-
- 3.1 where子句
-
- 3.1.1 检查单个值
- 3.1.2 不匹配检查
- 3.1.3 范围值检查
- 3.1.4 空值检查
- 第三章练习题
- 4. 高级数据过滤
-
- 4.1 组合where子句
-
- 4.1.1 and操作符
- 4.1.2 OR操作符
- 4.1.3 求值顺序
- 4.2 in操作符
- 4.3 not操作符
- 第四章练习题
- 5. 用通配符进行过滤
-
- 5.1 like操作符
-
- 5.1.1 百分号(%)通配符
- 5.1.2 下划线（_）通配符
- 5.1.3 方括号（[ ]）通配符
- 第五章练习题
- 6. 计算字段
-
- 6.1 算术字段
- 6.2 拼接字段
- 第六章练习题
- 7. 使用函数处理数据
-
- 7.1 文本处理函数
-
- 7.1.1 left()函数
- 7.1.2 lenth()函数
- 7.1.3 lower()函数
- 7.1.4 ltrim()函数
- 7.1.5 right()函数
- 7.1.6 rtrim()函数
- 7.1.7 substr()函数
- 7.1.8 soundex()函数
- 7.1.9 upper()函数
- 7.2 日期处理函数
- 7.3 数值处理函数
- 第七章练习题
- 8. 汇总数据
-
- 8.1 聚集函数
-
- 8.1.1 avg()函数
- 8.1.2 count()函数
- 8.1.3 max()函数
- 8.1.4 min()函数
- 8.1.5 sum()函数
- 8.2 组合聚集函数
- 第八章练习题
- 9. 分组数据
-
- 9.1 创建分组
- 9.2 过滤分组
- 9.3 分组和排序
- 第九章习题
- 10. 使用子查询
-
- 10.1 利用子查询进行过滤
- 10.2 作为计算字段使用子查询
- 第十章练习题
- 11. 联结表
-
- 11.1 创建联结
- 11.2 内联结
- 11.3 笛卡尔积
- 11.4 联结多个表
- 数据源
数据库结构图
sql5th
customers
orderitems
orders
vendors
表1：customers
表2：orderitems
表3：orders
表4：vendors
1. 检索数据
1.1 选择数据库
USE sql5th;
1.2 选择单列
select prod_name from Products;
+---------------------+
| prod_name |
+---------------------+
| Fish bean bag toy |
| Bird bean bag toy |
| Rabbit bean bag toy |
| 8 inch teddy bear |
| 12 inch teddy bear |
| 18 inch teddy bear |
| Raggedy Ann |
| King doll |
| Queen doll |
+---------------------+
9 rows in set
Time: 0.010s
1.3 选择多列
select prod_id, prod_name, prod_price from Products;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen doll | 9.49 |
+---------+---------------------+------------+
9 rows in set
Time: 0.006s
1.4 选择所有列
select * from Products;
1.5 检索不同的值
由下图可以看出产品供应商总共由3个，在我们查询的6个结果中含有重复的值。
select vend_id from products;
+---------+
| vend_id |
+---------+
| BRS01 |
| BRS01 |
| BRS01 |
| DLL01 |
| DLL01 |
| DLL01 |
| DLL01 |
| FNG01 |
| FNG01 |
+---------+
9 rows in set
Time: 0.006s
如果我们只想查询总共有多少供应商，我们应该怎么来写查询语句呢？
select distinct vend_id from Products;
+---------+
| vend_id |
+---------+
| BRS01 |
| DLL01 |
| FNG01 |
+---------+
3 rows in set
Time: 0.006s
select distinct vend_id, prod_price from Products;
从下图查询结果可以看出，当两列共同筛选唯一值时，只要每行数据都是唯一时，即可被筛选出来。
+---------+------------+
| vend_id | prod_price |
+---------+------------+
| DLL01 | 3.49 |
| BRS01 | 5.99 |
| BRS01 | 8.99 |
| BRS01 | 11.99 |
| DLL01 | 4.99 |
| FNG01 | 9.49 |
+---------+------------+
6 rows in set
Time: 0.006s
select vend_id, prod_price from Products;
+---------+------------+
| vend_id | prod_price |
+---------+------------+
| DLL01 | 3.49 |
| DLL01 | 3.49 |
| DLL01 | 3.49 |
| BRS01 | 5.99 |
| BRS01 | 8.99 |
| BRS01 | 11.99 |
| DLL01 | 4.99 |
| FNG01 | 9.49 |
| FNG01 | 9.49 |
+---------+------------+
9 rows in set
Time: 0.006s
1.6 限制结果
select prod_name from Products limit 5;
返回1-5行数据
+---------------------+
| prod_name |
+---------------------+
| Fish bean bag toy |
| Bird bean bag toy |
| Rabbit bean bag toy |
| 8 inch teddy bear |
| 12 inch teddy bear |
+---------------------+
5 rows in set
Time: 0.005s
返回5-10行数据
select prod_name from Products limit 5 offset 5;
+--------------------+
| prod_name |
+--------------------+
| 18 inch teddy bear |
| Raggedy Ann |
| King doll |
| Queen doll |
+--------------------+
4 rows in set
Time: 0.006s
1.7 注释
--单行注释
/*
多行注释
*/
第一章练习题
第一题
编写SQL语句，从Customers表中检索所有的ID（cust_id）。
select cust_id from Customers;
+------------+
| cust_id |
+------------+
| 1000000001 |
| 1000000002 |
| 1000000003 |
| 1000000004 |
| 1000000005 |
+------------+
5 rows in set
Time: 0.006s
第二题
OrderItems表包含了所有已订购的产品（有些已被订购多次）。编写SQL语句，检索并列出已订购产品（prod_id）的清单（不用列每个订单，只列出不同产品的清单）。提示：最终应该显示7行。
select distinct prod_id from OrderItems;
+---------+
| prod_id |
+---------+
| BNBG01 |
| BNBG02 |
| BNBG03 |
| BR01 |
| BR02 |
| BR03 |
| RGAN01 |
+---------+
7 rows in set
Time: 0.006s
第三题
编写SQL语句，检索Customers表中所有的列，再编写另外的SELECT语句，仅检索顾客的ID。使用注释，注释掉一条SELECT语句，以便运行另一条SELECT语句。（当然，要测试这两个语句。）
select * from Customers;
select cust_id from Customers;
+------------+
| cust_id |
+------------+
| 1000000001 |
| 1000000002 |
| 1000000003 |
| 1000000004 |
| 1000000005 |
+------------+
5 rows in set
Time: 0.005s
2. 排序检索数据
2.1 排序数据
select prod_name from Products order by prod_name;
对prod_name列以字母顺序排序数据的ORDER BY子句外，这条语句与前面的语句相同。
+---------------------+
| prod_name |
+---------------------+
| 12 inch teddy bear |
| 18 inch teddy bear |
| 8 inch teddy bear |
| Bird bean bag toy |
| Fish bean bag toy |
| King doll |
| Queen doll |
| Rabbit bean bag toy |
| Raggedy Ann |
+---------------------+
9 rows in set
Time: 0.006s
2.2 按多个列排序
select prod_id, prod_price, prod_name from Products order by prod_price,prod_name;
prod_price为第一排列顺序，prod_name为第二排列顺序。
+---------+------------+---------------------+
| prod_id | prod_price | prod_name |
+---------+------------+---------------------+
| BNBG02 | 3.49 | Bird bean bag toy |
| BNBG01 | 3.49 | Fish bean bag toy |
| BNBG03 | 3.49 | Rabbit bean bag toy |
| RGAN01 | 4.99 | Raggedy Ann |
| BR01 | 5.99 | 8 inch teddy bear |
| BR02 | 8.99 | 12 inch teddy bear |
| RYL01 | 9.49 | King doll |
| RYL02 | 9.49 | Queen doll |
| BR03 | 11.99 | 18 inch teddy bear |
+---------+------------+---------------------+
9 rows in set
Time: 0.006s
2.3 按排列位置排序
select prod_id, prod_price, prod_name from Products order by 2,3;
ORDER BY 2表示按SELECT清单中的第二个列prod_price进行排序。ORDER BY 2, 3表示先按prod_price，再按prod_name进行排序。
+---------+------------+---------------------+
| prod_id | prod_price | prod_name |
+---------+------------+---------------------+
| BNBG02 | 3.49 | Bird bean bag toy |
| BNBG01 | 3.49 | Fish bean bag toy |
| BNBG03 | 3.49 | Rabbit bean bag toy |
| RGAN01 | 4.99 | Raggedy Ann |
| BR01 | 5.99 | 8 inch teddy bear |
| BR02 | 8.99 | 12 inch teddy bear |
| RYL01 | 9.49 | King doll |
| RYL02 | 9.49 | Queen doll |
| BR03 | 11.99 | 18 inch teddy bear |
+---------+------------+---------------------+
9 rows in set
Time: 0.005s
2.4 指定排序方向
select prod_id, prod_price, prod_name from Products order by prod_price desc;
按照价格降序排列
+---------+------------+---------------------+
| prod_id | prod_price | prod_name |
+---------+------------+---------------------+
| BR03 | 11.99 | 18 inch teddy bear |
| RYL01 | 9.49 | King doll |
| RYL02 | 9.49 | Queen doll |
| BR02 | 8.99 | 12 inch teddy bear |
| BR01 | 5.99 | 8 inch teddy bear |
| RGAN01 | 4.99 | Raggedy Ann |
| BNBG01 | 3.49 | Fish bean bag toy |
| BNBG02 | 3.49 | Bird bean bag toy |
| BNBG03 | 3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
9 rows in set
Time: 0.005s
select prod_id, prod_price, prod_name from Products order by prod_price desc, prod_name;
按照价格降序排列，产品名称仍然按照标准的升序排列。
+---------+------------+---------------------+
| prod_id | prod_price | prod_name |
+---------+------------+---------------------+
| BR03 | 11.99 | 18 inch teddy bear |
| RYL01 | 9.49 | King doll |
| RYL02 | 9.49 | Queen doll |
| BR02 | 8.99 | 12 inch teddy bear |
| BR01 | 5.99 | 8 inch teddy bear |
| RGAN01 | 4.99 | Raggedy Ann |
| BNBG02 | 3.49 | Bird bean bag toy |
| BNBG01 | 3.49 | Fish bean bag toy |
| BNBG03 | 3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
9 rows in set
Time: 0.006s
第二章练习题
第一题
编写SQL语句，从Customers中检索所有的顾客名称（cust_names），并按从Z到A的顺序显示结果。
select cust_name from Customers order by cust_name desc;
+---------------+
| cust_name |
+---------------+
| Village Toys |
| The Toy Store |
| Kids Place |
| Fun4All |
| Fun4All |
+---------------+
5 rows in set
Time: 0.006s
第二题
编写SQL语句，从Orders表中检索顾客ID（cust_id）和订单号（order_num），并先按顾客ID对结果进行排序，再按订单日期倒序排列。
select cust_id, order_num from orders order by 1,2 desc;
-- 或者
select cust_id, order_num from orders order by cust_id, order_num desc;
+------------+-----------+
| cust_id | order_num |
+------------+-----------+
| 1000000001 | 20009 |
| 1000000001 | 20005 |
| 1000000003 | 20006 |
| 1000000004 | 20007 |
| 1000000005 | 20008 |
+------------+-----------+
5 rows in set
Time: 0.005s
第三题
显然，我们的虚拟商店更喜欢出售比较贵的物品，而且这类物品有很多。编写SQL语句，显示OrderItems表中的数量和价格（item_price），并按数量由多到少、价格由高到低排序。
select quantity, item_price from OrderItems order by quantity desc;
+----------+------------+
| quantity | item_price |
+----------+------------+
| 250 | 2.49 |
| 250 | 2.49 |
| 250 | 2.49 |
| 100 | 5.49 |
| 100 | 10.99 |
| 100 | 2.99 |
| 100 | 2.99 |
| 100 | 2.99 |
| 50 | 11.49 |
| 50 | 4.49 |
| 20 | 5.99 |
| 10 | 8.99 |
| 10 | 11.99 |
| 10 | 3.49 |
| 10 | 3.49 |
| 10 | 3.49 |
| 5 | 4.99 |
| 5 | 11.99 |
+----------+------------+
18 rows in set
Time: 0.005s
第四题
下面的SQL语句有问题吗？（尝试在不运行的情况下指出。）
select vend_name from Vendors order vend_name desc;
-- 正确语句
-- select vend_name from Vendors order by vend_name desc;
3. 过滤数据
3.1 where子句
select prod_name, prod_price from Products where prod_price = 3.49;
+---------------------+------------+
| prod_name | prod_price |
+---------------------+------------+
| Fish bean bag toy | 3.49 |
| Bird bean bag toy | 3.49 |
| Rabbit bean bag toy | 3.49 |
+---------------------+------------+
3 rows in set
Time: 0.005s
| 操作符 | 说明 | 操作符 | 说明 |
|---|---|---|---|
| = | 等于 | > | 大于 |
| <> | 不等于 | >= | 大于等于 |
| != | 不等于 | !> | 不大于 |
| < | 小于 | BETWEEN | 在指定的两个值之间 |
| <= | 小于等于 | IS NULL | 为NULL值 |
| !< | 不小于 |
3.1.1 检查单个值
select prod_name, prod_price from Products where prod_price < 10;
查询价格小于10美元的产品
+---------------------+------------+
| prod_name | prod_price |
+---------------------+------------+
| Fish bean bag toy | 3.49 |
| Bird bean bag toy | 3.49 |
| Rabbit bean bag toy | 3.49 |
| 8 inch teddy bear | 5.99 |
| 12 inch teddy bear | 8.99 |
| Raggedy Ann | 4.99 |
| King doll | 9.49 |
| Queen doll | 9.49 |
+---------------------+------------+
8 rows in set
Time: 0.005s
3.1.2 不匹配检查
select vend_id, prod_name from Products where vend_id <> "DLL01";
列出所有不是供应商DLL01制造的产品。
+---------+--------------------+
| vend_id | prod_name |
+---------+--------------------+
| BRS01 | 8 inch teddy bear |
| BRS01 | 12 inch teddy bear |
| BRS01 | 18 inch teddy bear |
| FNG01 | King doll |
| FNG01 | Queen doll |
+---------+--------------------+
5 rows in set
Time: 0.006s
3.1.3 范围值检查
select prod_name, prod_price from Products where prod_price between 5 and 10;
+--------------------+------------+
| prod_name | prod_price |
+--------------------+------------+
| 8 inch teddy bear | 5.99 |
| 12 inch teddy bear | 8.99 |
| King doll | 9.49 |
| Queen doll | 9.49 |
+--------------------+------------+
4 rows in set
Time: 0.005s
3.1.4 空值检查
select cust_name from Customers where cust_email is null;
+---------------+
| cust_name |
+---------------+
| Kids Place |
| The Toy Store |
+---------------+
2 rows in set
Time: 0.006s
第三章练习题
第一题
编写SQL语句，从Products表中检索产品ID（prod_id）和产品名称（prod_name），只返回价格为9.49美元的产品。
select prod_id, prod_name from Products where prod_price = 9.49;
+---------+------------+
| prod_id | prod_name |
+---------+------------+
| RYL01 | King doll |
| RYL02 | Queen doll |
+---------+------------+
2 rows in set
Time: 0.006s
第二题
编写SQL语句，从Products表中检索产品ID（prod_id）和产品名称（prod_name），只返回价格为9美元或更高的产品。
select prod_id, prod_name from Products where prod_price >= 9;
+---------+--------------------+
| prod_id | prod_name |
+---------+--------------------+
| BR03 | 18 inch teddy bear |
| RYL01 | King doll |
| RYL02 | Queen doll |
+---------+--------------------+
3 rows in set
Time: 0.006s
第三题
结合第3课和第4课编写SQL语句，从OrderItems表中检索出所有不同订单号（order_num），其中包含100个或更多的产品。
select distinct order_num from OrderItems where order_num >=100;
+-----------+
| order_num |
+-----------+
| 20005 |
| 20006 |
| 20007 |
| 20008 |
| 20009 |
+-----------+
5 rows in set
Time: 0.006s
第四题
编写SQL语句，返回Products表中所有价格在3美元到6美元之间的产品的名称（prod_name）和价格（prod_price），然后按价格对结果进行排序。（本题有多种解决方案，我们在下一课再讨论，不过你可以使用目前已学的知识来解决它。）
select prod_name, prod_price from Products where prod_price between 3 and 6 order by prod_price;
+---------------------+------------+
| prod_name | prod_price |
+---------------------+------------+
| Fish bean bag toy | 3.49 |
| Bird bean bag toy | 3.49 |
| Rabbit bean bag toy | 3.49 |
| Raggedy Ann | 4.99 |
| 8 inch teddy bear | 5.99 |
+---------------------+------------+
5 rows in set
Time: 0.005s
4. 高级数据过滤
4.1 组合where子句
4.1.1 and操作符
多个条件进行过滤，用在WHERE子句中的关键字，用来指示检索满足所有给定条件的行。
select prod_id, prod_price, prod_name from Products where vend_id = "DLL01" and prod_price <= 4;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name |
+---------+------------+---------------------+
| BNBG01 | 3.49 | Fish bean bag toy |
| BNBG02 | 3.49 | Bird bean bag toy |
| BNBG03 | 3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
3 rows in set
Time: 0.006s
4.1.2 OR操作符
WHERE子句中使用的关键字，用来表示检索匹配任一给定条件的行。
select prod_id, prod_price, prod_name from Products where vend_id = "DLL01" or vend_id ="BRS01";
+---------+------------+---------------------+
| prod_id | prod_price | prod_name |
+---------+------------+---------------------+
| BR01 | 5.99 | 8 inch teddy bear |
| BR02 | 8.99 | 12 inch teddy bear |
| BR03 | 11.99 | 18 inch teddy bear |
| BNBG01 | 3.49 | Fish bean bag toy |
| BNBG02 | 3.49 | Bird bean bag toy |
| BNBG03 | 3.49 | Rabbit bean bag toy |
| RGAN01 | 4.99 | Raggedy Ann |
+---------+------------+---------------------+
7 rows in set
Time: 0.006s
4.1.3 求值顺序
select prod_name, prod_price from Products where vend_id = "DLL01" or vend_id = "BRS01" and prod_price >= 10;
+---------------------+------------+
| prod_name | prod_price |
+---------------------+------------+
| 18 inch teddy bear | 11.99 |
| Fish bean bag toy | 3.49 |
| Bird bean bag toy | 3.49 |
| Rabbit bean bag toy | 3.49 |
| Raggedy Ann | 4.99 |
+---------------------+------------+
5 rows in set
Time: 0.006s
select prod_name, prod_price from Products where (vend_id = "DLL01" or vend_id = "BRS01") and prod_price >= 10;
+--------------------+------------+
| prod_name | prod_price |
+--------------------+------------+
| 18 inch teddy bear | 11.99 |
+--------------------+------------+
1 row in set
Time: 0.005s
计算机逻辑运算符优先级not > and > or
4.2 in操作符
select prod_name, prod_price from Products where vend_id in("DLL01","BRS01") order by prod_name;
-- 或者
select prod_name, prod_price from Products where vend_id = "DLL01" or vend_id = "BRS01" order by prod_name;
+---------------------+------------+
| prod_name | prod_price |
+---------------------+------------+
| 12 inch teddy bear | 8.99 |
| 18 inch teddy bear | 11.99 |
| 8 inch teddy bear | 5.99 |
| Bird bean bag toy | 3.49 |
| Fish bean bag toy | 3.49 |
| Rabbit bean bag toy | 3.49 |
| Raggedy Ann | 4.99 |
+---------------------+------------+
7 rows in set
Time: 0.006s
4.3 not操作符
WHERE子句中用来否定其后条件的关键字。
select prod_name from Products where not vend_id = "DLL01" order by prod_name;
-- 或者
select prod_name from Products where vend_id <> "DLL01" order by prod_name;
+--------------------+
| prod_name |
+--------------------+
| 12 inch teddy bear |
| 18 inch teddy bear |
| 8 inch teddy bear |
| King doll |
| Queen doll |
+--------------------+
5 rows in set
Time: 0.006s
第四章练习题
第一题
编写SQL语句，从Vendors表中检索供应商名称（vend_name），仅返回加利福尼亚州的供应商（这需要按国家[USA]和州[CA]进行过滤，没准其他国家也存在一个加利福尼亚州）。提示：过滤器需要匹配字符串。
select vend_name from Vendors where vend_state = "CA" and vend_country = "USA";
+-----------------+
| vend_name |
+-----------------+
| Doll House Inc. |
+-----------------+
1 row in set
Time: 0.006s
第二题
编写SQL语句，查找所有至少订购了总量100个的BR01、BR02或BR03的订单。你需要返回OrderItems表的订单号（order_num）、产品ID（prod_id）和数量，并按产品ID和数量进行过滤。提示：根据编写过滤器的方式，可能需要特别注意求值顺序。
select order_num, prod_id,quantity from OrderItems where quantity >= 100;
+-----------+---------+----------+
| order_num | prod_id | quantity |
+-----------+---------+----------+
| 20005 | BR01 | 100 |
| 20005 | BR03 | 100 |
| 20007 | BNBG01 | 100 |
| 20007 | BNBG02 | 100 |
| 20007 | BNBG03 | 100 |
| 20009 | BNBG01 | 250 |
| 20009 | BNBG02 | 250 |
| 20009 | BNBG03 | 250 |
+-----------+---------+----------+
8 rows in set
Time: 0.005s
第三题
现在，我们回顾上一课的挑战题。编写SQL语句，返回所有价格在3美元到6美元之间的产品的名称（prod_name）和价格（prod_price）。使用AND，然后按价格对结果进行排序。
select prod_name, prod_price from Products where prod_price between 3 and 6;
+---------------------+------------+
| prod_name | prod_price |
+---------------------+------------+
| Fish bean bag toy | 3.49 |
| Bird bean bag toy | 3.49 |
| Rabbit bean bag toy | 3.49 |
| 8 inch teddy bear | 5.99 |
| Raggedy Ann | 4.99 |
+---------------------+------------+
5 rows in set
Time: 0.007s
第四题
下面的SQL语句有问题吗？（尝试在不运行的情况下指出。）
select vend_name from Vendors order by vend_name where vend_country = "USA" and vend_state = "CA";
-- 修改
select vend_name from Vendors where vend_country = "USA" and vend_state = "CA" order by vend_name;
5. 用通配符进行过滤
**通配符（wildcard）**用来匹配值的一部分的特殊字符。
**搜索模式（search pattern）**由字面值、通配符或两者组合构成的搜索条件。
5.1 like操作符
5.1.1 百分号(%)通配符
| 符号 | 作用 |
|---|---|
%str |
匹配以str结尾的字符串 |
str% |
匹配以str开头的字符串 |
%str% |
匹配含有str的字符串 |
str区分大小写
select prod_id, prod_name from Products where prod_name like "Fish%";
+---------+-------------------+
| prod_id | prod_name |
+---------+-------------------+
| BNBG01 | Fish bean bag toy |
+---------+-------------------+
1 row in set
Time: 0.006s
select prod_id, prod_name from Products where prod_name like "%bean bag%";
+---------+---------------------+
| prod_id | prod_name |
+---------+---------------------+
| BNBG01 | Fish bean bag toy |
| BNBG02 | Bird bean bag toy |
| BNBG03 | Rabbit bean bag toy |
+---------+---------------------+
3 rows in set
Time: 0.005s
select prod_id, prod_name from Products where prod_name like "F%y";
+---------+-------------------+
| prod_id | prod_name |
+---------+-------------------+
| BNBG01 | Fish bean bag toy |
+---------+-------------------+
1 row in set
Time: 0.005s
如果某列文本字段有20个字符，而存储的文本为Fish beanbag toy（17个字符），则为填满该列需要在文本后附加3个空格。这样做一般对数据及其使用没有影响，但是可能对上述SQL语句有负面影响。子句WHERE prod_name LIKE 'F%y’只匹配以F开头、以y结尾的prod_name。如果值后面跟空格，则不是以y结尾，所以Fish beanbag toy就不会检索出来。简单的解决办法是给搜索模式再增加一个%号：'F%y%’还匹配y之后的字符（或空格）。通配符%不匹配NULL值。
5.1.2 下划线（_）通配符
下划线（_）的用途与%一样，但它只匹配单个字符，而不是多个字符。
select prod_id, prod_name from Products where prod_name like "__ inch teddy bear";
+---------+--------------------+
| prod_id | prod_name |
+---------+--------------------+
| BR02 | 12 inch teddy bear |
| BR03 | 18 inch teddy bear |
+---------+--------------------+
2 rows in set
Time: 0.005s
5.1.3 方括号（[ ]）通配符
方括号（[]）通配符用来指定一个字符集，它必须匹配指定位置（通配符的位置）的一个字符，[^str]表示不含str的字符串。
| 支持 | 不支持 |
|---|---|
SQL Server |
MySQL,Oracle,DB2,SQLite |
第五章练习题
第一题
编写SQL语句，从Products表中检索产品名称（prod_name）和描述（prod_desc），仅返回描述中包含toy一词的产品。
select prod_name, prod_desc from Products where prod_desc like "%toy%";
+---------------------+-----------------------------------------------------------------------+
| prod_name | prod_desc |
+---------------------+-----------------------------------------------------------------------+
| Fish bean bag toy | Fish bean bag toy, complete with bean bag worms with which to feed it |
| Bird bean bag toy | Bird bean bag toy, eggs are not included |
| Rabbit bean bag toy | Rabbit bean bag toy, comes with bean bag carrots |
+---------------------+-----------------------------------------------------------------------+
3 rows in set
Time: 0.006s
第二题
反过来再来一次。编写SQL语句，从Products表中检索产品名称（prod_name）和描述（prod_desc），仅返回描述中未出现toy一词的产品。这次，按产品名称对结果进行排序。
--演示数据库为MySQL,不支持`[]`通配符，故换另一种方式演示。
select prod_name, prod_desc from Products where prod_desc not like "%toy%";
+--------------------+--------------------------------------------------+
| prod_name | prod_desc |
+--------------------+--------------------------------------------------+
| 8 inch teddy bear | 8 inch teddy bear, comes with cap and jacket |
| 12 inch teddy bear | 12 inch teddy bear, comes with cap and jacket |
| 18 inch teddy bear | 18 inch teddy bear, comes with cap and jacket |
| Raggedy Ann | 18 inch Raggedy Ann doll |
| King doll | 12 inch king doll with royal garments and crown |
| Queen doll | 12 inch queen doll with royal garments and crown |
+--------------------+--------------------------------------------------+
6 rows in set
Time: 0.005s
第三题
编写SQL语句，从Products表中检索产品名称（prod_name）和描述（prod_desc），仅返回描述中同时出现toy和carrots的产品。有好几种方法可以执行此操作，但对于这个挑战题，请使用AND和两个LIKE比较。
select prod_name, prod_desc from Products where prod_desc like "%toy%" and prod_desc like "%carrots%";
+---------------------+--------------------------------------------------+
| prod_name | prod_desc |
+---------------------+--------------------------------------------------+
| Rabbit bean bag toy | Rabbit bean bag toy, comes with bean bag carrots |
+---------------------+--------------------------------------------------+
1 row in set
Time: 0.006s
第四题
来个比较棘手的。我没有特别向你展示这个语法，而是想看看你根据目前已学的知识是否可以找到答案。编写SQL语句，从Products表中检索产品名称（prod_name）和描述（prod_desc），仅返回在描述中以先后顺序同时出现toy和carrots的产品。提示：只需要用带有三个%符号的LIKE即可。
select prod_name, prod_desc from Products where prod_desc like "%toy%carrots%";
+---------------------+--------------------------------------------------+
| prod_name | prod_desc |
+---------------------+--------------------------------------------------+
| Rabbit bean bag toy | Rabbit bean bag toy, comes with bean bag carrots |
+---------------------+--------------------------------------------------+
1 row in set
Time: 0.005s
6. 计算字段
6.1 算术字段
检索订单号20008中的所有物品。
select prod_id, quantity, item_price from orderitems where order_num = 20008;
+---------+----------+------------+
| prod_id | quantity | item_price |
+---------+----------+------------+
| RGAN01 | 5 | 4.99 |
| BR03 | 5 | 11.99 |
| BNBG01 | 10 | 3.49 |
| BNBG02 | 10 | 3.49 |
| BNBG03 | 10 | 3.49 |
+---------+----------+------------+
5 rows in set
Time: 0.006s
汇总物品价格。
select prod_id, quantity, item_price, quantity * item_price as expanded_price from orderitems where order_num = 20008;
+---------+----------+------------+----------------+
| prod_id | quantity | item_price | expanded_price |
+---------+----------+------------+----------------+
| RGAN01 | 5 | 4.99 | 24.95 |
| BR03 | 5 | 11.99 | 59.95 |
| BNBG01 | 10 | 3.49 | 34.90 |
| BNBG02 | 10 | 3.49 | 34.90 |
| BNBG03 | 10 | 3.49 | 34.90 |
+---------+----------+------------+----------------+
5 rows in set
Time: 0.005
6.2 拼接字段
select concat(vend_name, "(",vend_country, ")") from vendors order by vend_name;
+------------------------------------------+
| concat(vend_name, "(",vend_country, ")") |
+------------------------------------------+
| Bear Emporium(USA) |
| Bears R Us(USA) |
| Doll House Inc.(USA) |
| Fun and Games(England) |
| Furball Inc.(USA) |
| Jouets et ours(France) |
+------------------------------------------+
6 rows in set
Time: 0.006s
第六章练习题
第一题
别名的常见用法是在检索出的结果中重命名表的列字段（为了符合特定的报表要求或客户需求）。编写SQL语句，从Vendors表中检索vend_id、vend_name、vend_address和vend_city，将vend_name重命名为vname，将vend_city重命名为vcity，将vend_address重命名为vaddress。按供应商名称对结果进行排序（可以使用原始名称或新的名称）。
select vend_id, vend_name as vname, vend_address as vaddress, vend_city as vcity from vendors order by vname;
+---------+-----------------+-----------------+------------+
| vend_id | vname | vaddress | vcity |
+---------+-----------------+-----------------+------------+
| BRE02 | Bear Emporium | 500 Park Street | Anytown |
| BRS01 | Bears R Us | 123 Main Street | Bear Town |
| DLL01 | Doll House Inc. | 555 High Street | Dollsville |
| FNG01 | Fun and Games | 42 Galaxy Road | London |
| FRB01 | Furball Inc. | 1000 5th Avenue | New York |
| JTS01 | Jouets et ours | 1 Rue Amusement | Paris |
+---------+-----------------+-----------------+------------+
6 rows in set
Time: 0.006s
第二题
我们的示例商店正在进行打折促销，所有产品均降价10%。编写SQL语句，从Products表中返回prod_id、prod_price和sale_price。sale_price是一个包含促销价格的计算字段。提示：可以乘以0.9，得到原价的90%（即10%的折扣）。
select prod_id, prod_price, prod_price * 0.9 as sale_price from products;
+---------+------------+------------+
| prod_id | prod_price | sale_price |
+---------+------------+------------+
| BNBG01 | 3.49 | 3.141 |
| BNBG02 | 3.49 | 3.141 |
| BNBG03 | 3.49 | 3.141 |
| BR01 | 5.99 | 5.391 |
| BR02 | 8.99 | 8.091 |
| BR03 | 11.99 | 10.791 |
| RGAN01 | 4.99 | 4.491 |
| RYL01 | 9.49 | 8.541 |
| RYL02 | 9.49 | 8.541 |
+---------+------------+------------+
9 rows in set
Time: 0.005s
7. 使用函数处理数据
7.1 文本处理函数
| 函数 | 说明 |
|---|---|
left() |
返回字符串左边的字符串 |
length(),datalength(),len() |
返回字符串的长度 |
lower() |
将字符串转换为小写 |
ltrim() |
去掉字符串左边的空格 |
right() |
返回字符串右边的字符 |
rtrim() |
去掉字符串右边的空格 |
substr(),substring() |
提取字符串的组成部分 |
sounddex() |
返回字符串的soundex值 |
upper() |
将字符串转换为大写 |
7.1.1 left()函数
select left(vend_name,3) from vendors;
+-------------------+
| left(vend_name,3) |
+-------------------+
| Bea |
| Bea |
| Dol |
| Fun |
| Fur |
| Jou |
+-------------------+
6 rows in set
Time: 0.006s
7.1.2 lenth()函数
select length(vend_name) from vendors;
+-------------------+
| left(vend_name,3) |
+-------------------+
| Bea |
| Bea |
| Dol |
| Fun |
| Fur |
| Jou |
+-------------------+
6 rows in set
Time: 0.005s
7.1.3 lower()函数
select lower(vend_name) from vendors;
+------------------+
| lower(vend_name) |
+------------------+
| bear emporium |
| bears r us |
| doll house inc. |
| fun and games |
| furball inc. |
| jouets et ours |
+------------------+
6 rows in set
Time: 0.006s
7.1.4 ltrim()函数
select ltrim(vend_name) from vendors;
+------------------+
| ltrim(vend_name) |
+------------------+
| Bear Emporium |
| Bears R Us |
| Doll House Inc. |
| Fun and Games |
| Furball Inc. |
| Jouets et ours |
+------------------+
6 rows in set
Time: 0.005s
7.1.5 right()函数
select right(vend_name,3) from vendors;
+--------------------+
| right(vend_name,3) |
+--------------------+
| ium |
| Us |
| nc. |
| mes |
| nc. |
| urs |
+--------------------+
6 rows in set
Time: 0.005s
7.1.6 rtrim()函数
select rtrim(vend_name) from vendors;
+------------------+
| rtrim(vend_name) |
+------------------+
| Bear Emporium |
| Bears R Us |
| Doll House Inc. |
| Fun and Games |
| Furball Inc. |
| Jouets et ours |
+------------------+
6 rows in set
Time: 0.005s
7.1.7 substr()函数
-- 提取字符串第三个字符（含）及之后的部分
select substr(vend_name,3) from vendors;
+---------------------+
| substr(vend_name,3) |
+---------------------+
| ar Emporium |
| ars R Us |
| ll House Inc. |
| n and Games |
| rball Inc. |
| uets et ours |
+---------------------+
6 rows in set
Time: 0.006s
7.1.8 soundex()函数
-- 查找发音相似的字符串
select cust_name, cust_contact from customers where soundex(cust_contact) = soundex("Michael Green");
+------------+----------------+
| cust_name | cust_contact |
+------------+----------------+
| Kids Place | Michelle Green |
+------------+----------------+
1 row in set
Time: 0.006s
7.1.9 upper()函数
select vend_name, upper(vend_name) as vend_name_name_upcase from vendors order by vend_name;
+-----------------+-----------------------+
| vend_name | vend_name_name_upcase |
+-----------------+-----------------------+
| Bear Emporium | BEAR EMPORIUM |
| Bears R Us | BEARS R US |
| Doll House Inc. | DOLL HOUSE INC. |
| Fun and Games | FUN AND GAMES |
| Furball Inc. | FURBALL INC. |
| Jouets et ours | JOUETS ET OURS |
+-----------------+-----------------------+
6 rows in set
Time: 0.006s
7.2 日期处理函数
select order_num from orders where year(order_date) = 2020;
+-----------+
| order_num |
+-----------+
| 20005 |
| 20006 |
| 20007 |
| 20008 |
| 20009 |
+-----------+
5 rows in set
Time: 0.006s
7.3 数值处理函数
| 函数 | 说明 |
|---|---|
abs() |
返回一个数的绝对值 |
cos() |
返回一个角度的余弦 |
exp() |
返回一个数的指数值 |
pi() |
返回圆周率 π \pi π的值 |
sin() |
返回一个角度的正弦 |
sqrt() |
返回一个数的平方根 |
tan() |
返回一个角度的正切 |
第七章练习题
第一题
所有用户都需要登录名，默认登录名是其名称和所在城市的组合。编写SQL语句，返回顾客ID（cust_id）、顾客名称（customer_name）和登录名（user_login），其中登录名全部为大写字母，并由顾客联系人的前两个字符（cust_contact）和其所在城市的前三个字符（cust_city）组成。例如，我的登录名是BEOAK（Ben Forta，居住在Oak Park）。提示：需要使用函数、拼接和别名。
select cust_id, cust_name as customer_name, upper(concat(left(cust_contact,2),left(cust_city,3))) as user_login from customers;
+------------+---------------+------------+
| cust_id | customer_name | user_login |
+------------+---------------+------------+
| 1000000001 | Village Toys | JODET |
| 1000000002 | Kids Place | MICOL |
| 1000000003 | Fun4All | JIMUN |
| 1000000004 | Fun4All | DEPHO |
| 1000000005 | The Toy Store | KICHI |
+------------+---------------+------------+
5 rows in set
Time: 0.007s
第二题
编写SQL语句，返回2020年1月的所有订单的订单号（order_num）和订单日期（order_date），并按订单日期排序。你应该能够根据目前已学的知识来解决此问题，但也可以开卷查阅DBMS文档。
select order_num, order_date from orders where year(order_date) = 2020 and month(order_date) = 01;
+-----------+---------------------+
| order_num | order_date |
+-----------+---------------------+
| 20006 | 2020-01-12 00:00:00 |
| 20007 | 2020-01-30 00:00:00 |
+-----------+---------------------+
2 rows in set
Time: 0.006s
8. 汇总数据
8.1 聚集函数
| 函数 | 说明 |
|---|---|
avg() |
返回某列的平均值 |
count() |
返回某列的行数 |
max() |
返回某列的最大值 |
min() |
返回某列的最小值 |
sum |
返回某列值之和 |
8.1.1 avg()函数
-- avg()函数忽略null值
select avg(prod_price) as avg_price from products;
+-----------+
| avg_price |
+-----------+
| 6.823333 |
+-----------+
1 row in set
Time: 0.005s
8.1.2 count()函数
count(*)包含所有行。count(colnm)忽略含有null值
select count(*) as num_cust from customers;
+----------+
| num_cust |
+----------+
| 5 |
+----------+
1 row in set
Time: 0.009s
select count(cust_email) as num_cust from customers;
+----------+
| num_cust |
+----------+
| 3 |
+----------+
1 row in set
Time: 0.006s
8.1.3 max()函数
-- max()忽略null值
select max(prod_price) as max_price from products;
+-----------+
| max_price |
+-----------+
| 11.99 |
+-----------+
1 row in set
Time: 0.006s
8.1.4 min()函数
同max()
8.1.5 sum()函数
-- sum()忽略null值
select sum(quantity) as items_ordered from orderitems where order_num = 20005;
+---------------+
| items_ordered |
+---------------+
| 200 |
+---------------+
1 row in set
Time: 0.006s
8.2 组合聚集函数
select count(*) as num_items, min(prod_price) as price_min, max(prod_price) as price_max, avg(prod_price) as price_avg from products;
+-----------+-----------+-----------+-----------+
| num_items | price_min | price_max | price_avg |
+-----------+-----------+-----------+-----------+
| 9 | 3.49 | 11.99 | 6.823333 |
+-----------+-----------+-----------+-----------+
1 row in set
Time: 0.006s
第八章练习题
第一题
编写SQL语句，确定已售出产品的总数（使用OrderItems中的quantity列）。
select sum(quantity) from orderitems;
+---------------+
| sum(quantity) |
+---------------+
| 1430 |
+---------------+
1 row in set
Time: 0.006s
第二题
修改刚刚创建的语句，确定已售出产品项（prod_item）BR01的总数。
select sum(order_item) from orderitems where prod_id = "BR01";
+-----------------+
| sum(order_item) |
+-----------------+
| 2 |
+-----------------+
1 row in set
Time: 0.006s
第三题
编写SQL语句，确定Products表中价格不超过10美元的最贵产品的价格（prod_price）。将计算所得的字段命名为max_price。
select max(prod_price) as max_price from products where prod_price <= 10;
+-----------+
| max_price |
+-----------+
| 9.49 |
+-----------+
1 row in set
Time: 0.006s
9. 分组数据
9.1 创建分组
select vend_id, count(*) as num_prods from products group by vend_id;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
| BRS01 | 3 |
| DLL01 | 4 |
| FNG01 | 2 |
+---------+-----------+
3 rows in set
Time: 0.005s
9.2 过滤分组
说明：HAVING和WHERE的差别这里有另一种理解方法，WHERE在数据分组前进行过滤，HAVING在数据分组后进行过滤。这是一个重要的区别，WHERE排除的行不包括在分组中。这可能会改变计算值，从而影响HAVING子句中基于这些值过滤掉的分组。
select cust_id, count(*) as orders from orders group by cust_id having count(*) >= 2;
+------------+--------+
| cust_id | orders |
+------------+--------+
| 1000000001 | 2 |
+------------+--------+
1 row in set
Time: 0.005s
select vend_id, count(*) as num_prods from products where prod_price >=4 group by vend_id having count(*) >= 2;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
| BRS01 | 3 |
| FNG01 | 2 |
+---------+-----------+
2 rows in set
Time: 0.007s
select vend_id, count(*) as num_prods from products where prod_price >= 4 group by vend_id having count(*) >= 2;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
| BRS01 | 3 |
| FNG01 | 2 |
+---------+-----------+
2 rows in set
Time: 0.006s
9.3 分组和排序
select order_num, count(*) as items from orderitems group by order_num having count(*) >= 3 order by items, order_num;
+-----------+-------+
| order_num | items |
+-----------+-------+
| 20006 | 3 |
| 20009 | 3 |
| 20007 | 5 |
| 20008 | 5 |
+-----------+-------+
4 rows in set
Time: 0.006s
第九章习题
第一题
OrderItems表包含每个订单的每个产品。编写SQL语句，返回每个订单号（order_num）各有多少行数（order_lines），并按order_lines对结果进行排序。
select order_num, count(*) as order_lines from orderitems group by order_num order by order_lines;
+-----------+-------------+
| order_num | order_lines |
+-----------+-------------+
| 20005 | 2 |
| 20006 | 3 |
| 20009 | 3 |
| 20007 | 5 |
| 20008 | 5 |
+-----------+-------------+
5 rows in set
Time: 0.006s
第二题
编写SQL语句，返回名为cheapest_item的字段，该字段包含每个供应商成本最低的产品（使用Products表中的prod_price），然后从最低成本到最高成本对结果进行排序。
select min(prod_price) as cheapest_item from products group by vend_id;
+---------------+
| cheapest_item |
+---------------+
| 5.99 |
| 3.49 |
| 9.49 |
+---------------+
3 rows in set
Time: 0.006s
第三题
确定最佳顾客非常重要，请编写SQL语句，返回至少含100项的所有订单的订单号（OrderItems表中的order_num）。
select order_num, sum(quantity) as sum_quantity from orderitems group by order_num having sum_quantity >= 100 ;
+-----------+--------------+
| order_num | sum_quantity |
+-----------+--------------+
| 20005 | 200 |
| 20007 | 400 |
| 20009 | 750 |
+-----------+--------------+
3 rows in set
Time: 0.006s
第四题
确定最佳顾客的另一种方式是看他们花了多少钱。编写SQL语句，返回总价至少为1000的所有订单的订单号（OrderItems表中的order_num）。提示：需要计算总和（item_price乘以quantity）。按订单号对结果进行排序。
select order_num, sum(item_price * quantity) as total from orderitems group by order_num having total >= 1000 order by order_num;
+-----------+---------+
| order_num | total |
+-----------+---------+
| 20005 | 1648.00 |
| 20007 | 1696.00 |
| 20009 | 1867.50 |
+-----------+---------+
3 rows in set
Time: 0.006s
第五题
下面的SQL语句有问题吗？（尝试在不运行的情况下指出。）
-- count(*)不能通过group by 进行分组
select order_num, count(*) as items from orderitems group by items having count(*) >= 3 order by items. order_num;
10. 使用子查询
10.1 利用子查询进行过滤
列出订购物品RGAN01的所有顾客。
- 第一步检索包含物品RGAN01的所有订单的编号。
- 第二步检索具有前一步骤列出的订单编号的所有顾客的ID。
- 第三步检索前一步骤返回的所有顾客ID的顾客信息。
-- 第一步
select order_num from orderitems where prod_id = "RGAN01";
+-----------+
| order_num |
+-----------+
| 20007 |
| 20008 |
+-----------+
2 rows in set
Time: 0.006s
-- 第二步
select cust_id from orders where order_num in (20007,20008);
+------------+
| cust_id |
+------------+
| 1000000004 |
| 1000000005 |
+------------+
2 rows in set
Time: 0.005s
-- 第三步
select cust_name, cust_contact from customers where cust_id in (1000000004,1000000005);
+---------------+--------------------+
| cust_name | cust_contact |
+---------------+--------------------+
| Fun4All | Denise L. Stephens |
| The Toy Store | Kim Howard |
+---------------+--------------------+
2 rows in set
Time: 0.006s
通过嵌套子查询将以上三条语句合并为一条。
-- 嵌套子查询
select cust_name, cust_contact from customers where cust_id in(
select cust_id from orders where order_num in(
select order_num from orderitems where prod_id = "RGAN01"
));
+---------------+--------------------+
| cust_name | cust_contact |
+---------------+--------------------+
| Fun4All | Denise L. Stephens |
| The Toy Store | Kim Howard |
+---------------+--------------------+
2 rows in set
Time: 0.006s
10.2 作为计算字段使用子查询
查询Customers表中每个顾客的订单总数。
- 第一步从Customers表中检索顾客列表；
- 第二步对于检索出的每个顾客，统计其在Orders表中的订单数目。
-- 第一步
select count(*) as orders from orders where cust_id = 1000000001;
+--------+
| orders |
+--------+
| 2 |
+--------+
1 row in set
Time: 0.006s
-- 第二步
select cust_name, cust_state, (
select count(*) from orders where orders.cust_id = customers.cust_id
) as orders from customers order by cust_name;
+---------------+------------+--------+
| cust_name | cust_state | orders |
+---------------+------------+--------+
| Fun4All | IN | 1 |
| Fun4All | AZ | 1 |
| Kids Place | OH | 0 |
| The Toy Store | IL | 1 |
| Village Toys | MI | 2 |
+---------------+------------+--------+
5 rows in set
Time: 0.007s
第十章练习题
第一题
使用子查询，返回购买价格为10美元或以上产品的顾客列表。你需要使用OrderItems表查找匹配的订单号（order_num），然后使用Order表检索这些匹配订单的顾客ID（cust_id）。
select cust_name, cust_contact from customers where cust_id in (
select cust_id from orders where orders.order_num in (
select order_num from orderitems where item_price>=10));
+---------------+--------------------+
| cust_name | cust_contact |
+---------------+--------------------+
| Village Toys | John Smith |
| Fun4All | Jim Jones |
| Fun4All | Denise L. Stephens |
| The Toy Store | Kim Howard |
+---------------+--------------------+
4 rows in set
Time: 0.006s
第二题
你想知道订购BR01产品的日期。编写SQL语句，使用子查询来确定哪些订单（在OrderItems中）购买了prod_id为BR01的产品，然后从Orders表中返回每个产品对应的顾客ID（cust_id）和订单日期（order_date）。按订购日期对结果进行排序。
select cust_id, order_date from orders where order_num in (
select order_num from orderitems where prod_id = "BR01"
) order by order_date;
+------------+---------------------+
| cust_id | order_date |
+------------+---------------------+
| 1000000003 | 2020-01-12 00:00:00 |
| 1000000001 | 2020-05-01 00:00:00 |
+------------+---------------------+
2 rows in set
Time: 0.006s
第三题
现在我们让它更具挑战性。在上一个挑战题，返回购买prod_id为BR01的产品的所有顾客的电子邮件（Customers表中的cust_email）。提示：这涉及SELECT语句，最内层的从OrderItems表返回order_num，中间的从Customers表返回cust_id。
select cust_id, cust_email from customers where cust_id in (
select cust_id from orders where order_num in (
select order_num from orderitems where prod_id = "BR01"))
+------------+-----------------------+
| cust_id | cust_email |
+------------+-----------------------+
| 1000000001 | [email protected] |
| 1000000003 | [email protected] |
+------------+-----------------------+
2 rows in set
Time: 0.006s
第四题
我们需要一个顾客ID列表，其中包含他们已订购的总金额。编写SQL语句，返回顾客ID（Orders表中的cust_id），并使用子查询返回total_ordered以便返回每个顾客的订单总数。将结果按金额从大到小排序。提示：你之前已经使用SUM()计算订单总数。
select cust_id, (
select sum(item_price * quantity) from orderitems where orders.order_num = orderitems.order_num) as total_ordered
from orders order by total_ordered desc;
+------------+---------------+
| cust_id | total_ordered |
+------------+---------------+
| 1000000001 | 1867.50 |
| 1000000004 | 1696.00 |
| 1000000001 | 1648.00 |
| 1000000003 | 329.60 |
| 1000000005 | 189.60 |
+------------+---------------+
5 rows in set
Time: 0.007s
第五题
再来。编写SQL语句，从Products表中检索所有的产品名称（prod_name），以及名为quant_sold的计算列，其中包含所售产品的总数（在OrderItems表上使用子查询和SUM(quantity)检索）
select prod_name, (
select sum(quantity) from orderitems where orderitems.prod_id = products.prod_id
) as quant_sold from products;
+---------------------+------------+
| prod_name | quant_sold |
+---------------------+------------+
| Fish bean bag toy | 360 |
| Bird bean bag toy | 360 |
| Rabbit bean bag toy | 360 |
| 8 inch teddy bear | 120 |
| 12 inch teddy bear | 10 |
| 18 inch teddy bear | 165 |
| Raggedy Ann | 55 |
| King doll | |
| Queen doll | |
+---------------------+------------+
9 rows in set
Time: 0.005s
11. 联结表
11.1 创建联结
select vend_name, prod_name, prod_price from vendors, products where vendors.vend_id = products.vend_id;
+-----------------+---------------------+------------+
| vend_name | prod_name | prod_price |
+-----------------+---------------------+------------+
| Doll House Inc. | Fish bean bag toy | 3.49 |
| Doll House Inc. | Bird bean bag toy | 3.49 |
| Doll House Inc. | Rabbit bean bag toy | 3.49 |
| Bears R Us | 8 inch teddy bear | 5.99 |
| Bears R Us | 12 inch teddy bear | 8.99 |
| Bears R Us | 18 inch teddy bear | 11.99 |
| Doll House Inc. | Raggedy Ann | 4.99 |
| Fun and Games | King doll | 9.49 |
| Fun and Games | Queen doll | 9.49 |
+-----------------+---------------------+------------+
9 rows in set
Time: 0.006s
11.2 内联结
-- 查询结果同上
select vend_name, prod_name, prod_price from vendors inner join products on vendors.vend_id = products.vend_id;
+-----------------+---------------------+------------+
| vend_name | prod_name | prod_price |
+-----------------+---------------------+------------+
| Doll House Inc. | Fish bean bag toy | 3.49 |
| Doll House Inc. | Bird bean bag toy | 3.49 |
| Doll House Inc. | Rabbit bean bag toy | 3.49 |
| Bears R Us | 8 inch teddy bear | 5.99 |
| Bears R Us | 12 inch teddy bear | 8.99 |
| Bears R Us | 18 inch teddy bear | 11.99 |
| Doll House Inc. | Raggedy Ann | 4.99 |
| Fun and Games | King doll | 9.49 |
| Fun and Games | Queen doll | 9.49 |
+-----------------+---------------------+------------+
9 rows in set
Time: 0.006s
11.3 笛卡尔积
笛卡儿积（cartesian product）由没有联结条件的表关系返回的结果为笛卡儿积。检索出的行的数目将是第一个表中的行数乘以第二个表中的行数。
11.4 联结多个表
select prod_name, vend_name, prod_price, quantity from orderitems, products, vendors where products.vend_id = vendors.vend_id and orderitems.prod_id = products.prod_id and order_num = 20007;
+---------------------+-----------------+------------+----------+
| prod_name | vend_name | prod_price | quantity |
+---------------------+-----------------+------------+----------+
| 18 inch teddy bear | Bears R Us | 11.99 | 50 |
| Fish bean bag toy | Doll House Inc. | 3.49 | 100 |
| Bird bean bag toy | Doll House Inc. | 3.49 | 100 |
| Rabbit bean bag toy | Doll House Inc. | 3.49 | 100 |
| Raggedy Ann | Doll House Inc. | 4.99 | 50 |
+---------------------+-----------------+------------+----------+
5 rows in set
Time: 0.014s
下面我们通过联结表来解决10.1的问题。
select cust_name, cust_contact from customers, orders, orderitems where customers.cust_id = orders.cust_id and orderitems.order_num = orders.order_num and prod_id = "RGAN01";
+---------------+--------------------+
| cust_name | cust_contact |
+---------------+--------------------+
| Fun4All | Denise L. Stephens |
| The Toy Store | Kim Howard |
+---------------+--------------------+
2 rows in set
Time: 0.006s
数据源
-- Ceate
-- Sams Teach Yourself SQL in 10 Minutes, 5th Edition
-- http://forta.com/books/0135182794/
-- Example table creation scripts for MySQL & MariaDB
-- ----------------------
-- Create Customers table
-- ----------------------
CREATE TABLE Customers
(
cust_id char(10) NOT NULL ,
cust_name char(50) NOT NULL ,
cust_address char(50) NULL ,
cust_city char(50) NULL ,
cust_state char(5) NULL ,
cust_zip char(10) NULL ,
cust_country char(50) NULL ,
cust_contact char(50) NULL ,
cust_email char(255) NULL
);
-- -----------------------
-- Create OrderItems table
-- -----------------------
CREATE TABLE OrderItems
(
order_num int NOT NULL ,
order_item int NOT NULL ,
prod_id char(10) NOT NULL ,
quantity int NOT NULL ,
item_price decimal(8,2) NOT NULL
);
-- -------------------
-- Create Orders table
-- -------------------
CREATE TABLE Orders
(
order_num int NOT NULL ,
order_date datetime NOT NULL ,
cust_id char(10) NOT NULL
);
-- ---------------------
-- Create Products table
-- ---------------------
CREATE TABLE Products
(
prod_id char(10) NOT NULL ,
vend_id char(10) NOT NULL ,
prod_name char(255) NOT NULL ,
prod_price decimal(8,2) NOT NULL ,
prod_desc text NULL
);
-- --------------------
-- Create Vendors table
-- --------------------
CREATE TABLE Vendors
(
vend_id char(10) NOT NULL ,
vend_name char(50) NOT NULL ,
vend_address char(50) NULL ,
vend_city char(50) NULL ,
vend_state char(5) NULL ,
vend_zip char(10) NULL ,
vend_country char(50) NULL
);
-- -------------------
-- Define primary keys
-- -------------------
ALTER TABLE Customers ADD PRIMARY KEY (cust_id);
ALTER TABLE OrderItems ADD PRIMARY KEY (order_num, order_item);
ALTER TABLE Orders ADD PRIMARY KEY (order_num);
ALTER TABLE Products ADD PRIMARY KEY (prod_id);
ALTER TABLE Vendors ADD PRIMARY KEY (vend_id);
-- -------------------
-- Define foreign keys
-- -------------------
ALTER TABLE OrderItems ADD CONSTRAINT FK_OrderItems_Orders FOREIGN KEY (order_num) REFERENCES Orders (order_num);
ALTER TABLE OrderItems ADD CONSTRAINT FK_OrderItems_Products FOREIGN KEY (prod_id) REFERENCES Products (prod_id);
ALTER TABLE Orders ADD CONSTRAINT FK_Orders_Customers FOREIGN KEY (cust_id) REFERENCES Customers (cust_id);
ALTER TABLE Products ADD CONSTRAINT FK_Products_Vendors FOREIGN KEY (vend_id) REFERENCES Vendors (vend_id);
--Populate
-- Sams Teach Yourself SQL in 10 Minutes, 5th Edition
-- http://forta.com/books/0135182794/
-- Example table population scripts for MySQL & MariaDB
-- ------------------------
-- Populate Customers table
-- ------------------------
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES('1000000001', 'Village Toys', '200 Maple Lane', 'Detroit', 'MI', '44444', 'USA', 'John Smith', '[email protected]');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact)
VALUES('1000000002', 'Kids Place', '333 South Lake Drive', 'Columbus', 'OH', '43333', 'USA', 'Michelle Green');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES('1000000003', 'Fun4All', '1 Sunny Place', 'Muncie', 'IN', '42222', 'USA', 'Jim Jones', '[email protected]');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES('1000000004', 'Fun4All', '829 Riverside Drive', 'Phoenix', 'AZ', '88888', 'USA', 'Denise L. Stephens', '[email protected]');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact)
VALUES('1000000005', 'The Toy Store', '4545 53rd Street', 'Chicago', 'IL', '54545', 'USA', 'Kim Howard');
-- ----------------------
-- Populate Vendors table
-- ----------------------
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('BRS01','Bears R Us','123 Main Street','Bear Town','MI','44444', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('BRE02','Bear Emporium','500 Park Street','Anytown','OH','44333', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('DLL01','Doll House Inc.','555 High Street','Dollsville','CA','99999', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('FRB01','Furball Inc.','1000 5th Avenue','New York','NY','11111', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('FNG01','Fun and Games','42 Galaxy Road','London', NULL,'N16 6PS', 'England');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('JTS01','Jouets et ours','1 Rue Amusement','Paris', NULL,'45678', 'France');
-- -----------------------
-- Populate Products table
-- -----------------------
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BR01', 'BRS01', '8 inch teddy bear', 5.99, '8 inch teddy bear, comes with cap and jacket');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BR02', 'BRS01', '12 inch teddy bear', 8.99, '12 inch teddy bear, comes with cap and jacket');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BR03', 'BRS01', '18 inch teddy bear', 11.99, '18 inch teddy bear, comes with cap and jacket');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BNBG01', 'DLL01', 'Fish bean bag toy', 3.49, 'Fish bean bag toy, complete with bean bag worms with which to feed it');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BNBG02', 'DLL01', 'Bird bean bag toy', 3.49, 'Bird bean bag toy, eggs are not included');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BNBG03', 'DLL01', 'Rabbit bean bag toy', 3.49, 'Rabbit bean bag toy, comes with bean bag carrots');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('RGAN01', 'DLL01', 'Raggedy Ann', 4.99, '18 inch Raggedy Ann doll');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('RYL01', 'FNG01', 'King doll', 9.49, '12 inch king doll with royal garments and crown');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('RYL02', 'FNG01', 'Queen doll', 9.49, '12 inch queen doll with royal garments and crown');
-- ---------------------
-- Populate Orders table
-- ---------------------
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20005, '2020-05-01', '1000000001');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20006, '2020-01-12', '1000000003');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20007, '2020-01-30', '1000000004');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20008, '2020-02-03', '1000000005');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20009, '2020-02-08', '1000000001');
-- -------------------------
-- Populate OrderItems table
-- -------------------------
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20005, 1, 'BR01', 100, 5.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20005, 2, 'BR03', 100, 10.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20006, 1, 'BR01', 20, 5.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20006, 2, 'BR02', 10, 8.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20006, 3, 'BR03', 10, 11.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 1, 'BR03', 50, 11.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 2, 'BNBG01', 100, 2.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 3, 'BNBG02', 100, 2.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 4, 'BNBG03', 100, 2.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 5, 'RGAN01', 50, 4.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 1, 'RGAN01', 5, 4.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 2, 'BR03', 5, 11.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 3, 'BNBG01', 10, 3.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 4, 'BNBG02', 10, 3.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 5, 'BNBG03', 10, 3.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20009, 1, 'BNBG01', 250, 2.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20009, 2, 'BNBG02', 250, 2.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20009, 3, 'BNBG03', 250, 2.49);