Les08_处理数据.ppt

Rolling Back Changes Discard all pending changes by using the ROLLBACK statement. Following a ROLLBACK statement: Data changes are undone. The previous state of the data is restored. The locks on the affected rows are released. Example While attempting to remove a record from the TEST table, you can accidentally empty the table. You can correct the mistake, reissue the proper statement, and make the data change permanent. DELETE FROM test; 25,000 rows deleted. ROLLBACK; Rollback complete. DELETE FROM test WHERE id = 100; 1 row deleted. SELECT * FROM test WHERE id = 100; No rows selected. COMMIT; Commit complete. Summary In this lesson, you should have learned how to manipulate data in the Oracle database by using the INSERT, UPDATE, and DELETE statements. Control data changes by using the COMMIT, SAVEPOINT, and ROLLBACK statements. The Oracle server guarantees a consistent view of data at all times. Locking can be implicit or explicit. 数据库事务必须同时满足4个特性: 原子性(Atomic), 一致性(Consistency), 隔离性(Isolation)和持久性(Durabiliy), 简称为ACID 处理数据 目标 通过本章学习，您将可以: 使用 DML 语句 向表中插入数据 更新表中数据 从表中删除数据 控制事务 数据控制语言 DML(Data Manipulation Language – 数据操作语言) 可以在下列条件下执行: 向表中插入数据 修改现存数据 删除现存数据 事务是由完成若干项工作的DML语句组成的 插入数据 DEPARTMENTS 新行 向 DEPARMENTS 表中插入 新的记录 INSERT 语句语法 使用 INSERT 语句向表中插入数据。 使用这种语法一次只能向表中插入一条数据。 INSERT INTO table [(column [, column...])] VALUES (value [, value...]); 插入数据 为每一列添加一个新值。 按列的默认顺序列出各个列的值。 在 INSERT 子句中随意列出列名和他们的值。 字符和日期型数据应包含在单引号中。 INSERT INTO departments(department_id, department_name, manager_id, location_id) VALUES (70, Public Relations, 100, 1700); 1 row created. 向表中插入空值 隐式方式: 在列名表中省略该列的值。 INSERT INTO departments VALUES (100, Finance, NULL, NULL); 1 row created. INSERT INTO departments (department_id, department_name ) VALUES (30, Purchasing); 1 row created. 显示方式: 在VALUES 子句中指定空值。 插入指定的值 SYSDATE 记录当前系统的日期和时间。 INSERT INTO employees