关于火车站售票系统并发访问和锁机制问题？

如果一个用户对记录加锁，如何使其他用户看不到这条记录。[@more@]有人问到这样的问题:如果一个用户对记录加锁，如何使其他用户看不到这条记录。
此前并未注意到这样一个用法（需要8.1.7.4.16以上的版本支持）:

[oracle@jumper oracle]$ sqlplus scott/tiger SQL*Plus: Release 9.2.0.4.0 - Production on Fri Mar 4 11:59:46 2005 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production SQL> select * from dept; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON 33 ORACLE beijing 35 Oracle Beijing 36 Oracle Beijing 37 Oracle Beijing 8 rows selected. SQL> select * from dept where deptno =10 for update; DEPTNO DNAME LOC ---------- -------------- ------------- 10 ACCOUNTING NEW YORK SQL> ! [oracle@jumper oracle]$ sqlplus scott/tiger SQL*Plus: Release 9.2.0.4.0 - Production on Fri Mar 4 12:00:14 2005 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production SQL> select * from dept for update skip locked; DEPTNO DNAME LOC ---------- -------------- ------------- 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON 33 ORACLE beijing 35 Oracle Beijing 36 Oracle Beijing 37 Oracle Beijing 7 rows selected. SQL>

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