oracle表在什么情况下会被锁住

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

oracle 锁表的语句

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.

怎样在oracle 给表加锁？？

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

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