更新和删除数据

• 更新数据
• • 例1
  • 例2
  • 例3
• 删除数据
• • 例4
• 更新和删除的指导原则
• 小结
• 挑战题
• • 1
  • 2

更新数据

例1

UPDATE customers
SET cust_email='peng@orystore.com'
WHERE cust_id=1000000006;

例2

UPDATE customers
SET cust_contact='Sam Roberts',
	cust_email='Sam@toyland.com'
WHERE cust_id=1000000007;

例3

UPDATE customers
SET cust_email=NULL
WHERE cust_id=1000000005;

删除数据

例4

DELETE FROM customers
WHERE cust_id=1000000006;

更新和删除的指导原则

1. 除非真的要更新和删除每一行，否则绝对不要使用不带WHERE子句的UPDATE和DELETE语句
2. 保证每个表都有主键，尽量像WHERE子句那样使用
3. 在UPDATE或DELETE语句使用WHERE子句之前，应该先用SELECT进行测试，保证它过滤的是正确的行
4. 使用强制实施引用完整性的数据库
5. 如果使用的DBMS允许数据库管理员施加约束，防止执行不带WHERE子句的UPDATE或DELETE子句，使用它

小结

1. 如何使用UPDATE或DELETE语句处理表中的数据
2. 知道了可能存在的危险
3. 学习了为保证数据安全而应该遵循的一些指导原则

挑战题

1

USA State abbreviations should always be in upper case. Write a SQL statement to update all USA addresses, both vendor states (vend_state in Vendors) and customer states (cust_state in Customers) so that they are upper case.

UPDATE vendors
SET vend_state=UPPER(vend_state);

UPDATE customers
SET cust_state=UPPER(cust_state);

2

In Lesson 15 Challenge 1 I asked you to add yourself to the Customers table. Now delete yourself. Make sure to use a WHERE clause (and test it with a SELECT before using it in DELETE) or you’ll delete all customers!

SELECT * FROM customers
WHERE cust_id = 1000000009;

DELETE FROM customers
WHERE cust_id=1000000009;