在对指定表做append操作，其他再做truncate时候，会产生锁表，如下验证步骤，
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1、创建测试表，
create table test_lock(id number, value varchar2(200));
2、执行append语句；并且不做提交，insert /*+append*/ into test_lock values(1,1);
3、再次执行清表语句，truncate table test_lock;报锁表错误，
4、查看锁表语句，发现被锁表，
select b.object_name, t.*
from v$locked_object t, user_objects b
where t.object_id = b.object_id
lock table 表名 exclusive mode nowait; -- 锁整个表
select * from 表名 where XXX for update nowaitl -- 锁符合条件的记录
锁表：LOCK TABLE tablename IN 锁模式 MODE;
解锁：commit或rollback;
锁模式有以下几种：
ROW SHARE
ROW SHARE permits concurrent access to the locked table but prohibits users from locking the entire table for exclusive access. ROW SHARE is synonymous with SHARE UPDATE, which is included for compatibility with earlier versions of Oracle Database.
ROW EXCLUSIVE
ROW EXCLUSIVE is the same as ROW SHARE, but it also prohibits locking in SHARE mode. ROW EXCLUSIVE locks are automatically obtained when updating, inserting, or deleting.
SHARE UPDATE
See ROW SHARE.
SHARE
SHARE permits concurrent queries but prohibits updates to the locked table.
SHARE ROW EXCLUSIVE
SHARE ROW EXCLUSIVE is used to look at a whole table and to allow others to look at rows in the table but to prohibit others from locking the table in SHARE mode or from updating rows.
EXCLUSIVE
EXCLUSIVE permits queries on the locked table but prohibits any other activity on it.
1、在做Oracle监听程序测试时，发现帐户已经被锁定。
2、在数据库安装电脑上，点击开始打开运行窗口。
3、在运行窗口输入CMD，调出命令提示符界面。
3、在命令提示符下面，用管理员身份登入到数据库sqlplus / as sysdba。
4、输入解锁命令alter user Scott account unlock后回车。
5、看见用户已更改的字样，表示命令已成功执行。
6、再切换到监听程序验证，原来的ora-28000帐户被锁定的提示已经不存在了。用户解锁成功。
