- 1、本文档共48页,可阅读全部内容。
- 2、有哪些信誉好的足球投注网站(book118)网站文档一经付费(服务费),不意味着购买了该文档的版权,仅供个人/单位学习、研究之用,不得用于商业用途,未经授权,严禁复制、发行、汇编、翻译或者网络传播等,侵权必究。
- 3、本站所有内容均由合作方或网友上传,本站不对文档的完整性、权威性及其观点立场正确性做任何保证或承诺!文档内容仅供研究参考,付费前请自行鉴别。如您付费,意味着您自己接受本站规则且自行承担风险,本站不退款、不进行额外附加服务;查看《如何避免下载的几个坑》。如果您已付费下载过本站文档,您可以点击 这里二次下载。
- 4、如文档侵犯商业秘密、侵犯著作权、侵犯人身权等,请点击“版权申诉”(推荐),也可以打举报电话:400-050-0827(电话支持时间:9:00-18:30)。
查看更多
Oracle11g第06讲事务及锁课件
What Are Locks? Locks are mechanisms that prevent destructive interaction between transactions accessing the same resource, either a user object (such as tables or rows) or a system object not visible to users (such as shared data structures and data dictionary rows). How the Oracle Database Locks Data Oracle locking is performed automatically and requires no user action. Implicit locking occurs for SQL statements as necessary, depending on the action requested. Implicit locking occurs for all SQL statements except SELECT. The users can also lock data manually, which is called explicit locking. Instructor Note See the Instructor Note on 52. DML Locking When performing data manipulation language (DML) operations, the Oracle server provides data concurrency through DML locking. DML locks occur at two levels: A share lock is automatically obtained at the table level during DML operations. With share lock mode, several transactions can acquire share locks on the same resource. An exclusive lock is acquired automatically for each row modified by a DML statement. Exclusive locks prevent the row from being changed by other transactions until the transaction is committed or rolled back. This lock ensures that no other user can modify the same row at the same time and overwrite changes not yet committed by another user. DDL locks occur when you modify a database object such as a table. Instructor Note A SELECT...FOR UPDATE statement also implements a lock. This is covered in the Oracle9i PL/SQL course. 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. COMMIT; Commit complete. 改变数据 提交改变 DELETE FROM employees WHERE employee_id = 99999; 1 row deleted. INSERT INTO departm
您可能关注的文档
- Office2010培训课件.pptx
- 沟通技能培训班(潘习龙).ppt
- ON11沟通策略35.ppt
- 沥青路面变形类病害维护.ppt
- OLSR协议流程.ppt
- 沥青软化点试验.ppt
- Office2Excel.ppt
- OnSemiNCV7381单路FlexRay总线驱动解决方案.docx
- 沥青软化点使用说明书.doc
- 沉积岩2013.3.12.ppt
- 童趣风快乐阅读班会分享.pptx
- 《如何有效地听课和评课》--教师培训课件.ppt.pptx
- 【高分必刷】人教版一年级数学上册第八单元高频考点突破卷-含答案.pdf
- 【高分必刷】人教版一年级数学上册第三单元达标测试卷-含答案.pdf
- 【高分必刷】人教版一年级数学上册五6~10的认识和加减法第五课时10一课一练课时练-含答案.pdf
- 高考英语3500词汇表-带音标.pdf
- 【高分必刷】人教版一年级数学上册第二单元过关检测卷-含答案.pdf
- 2024-2025年北师大版数学选择性必修第一册6.1.2-1.3乘法公式、全概率公式(带答案).docx
- 2024-2025年北师大版数学必修第一册7.1.4随机事件的运算(带答案).docx
- 2024-2025年北师大版数学选择性必修第一册6.4.1二项分布(带答案).docx
文档评论(0)