Oracle设置表只读－alter table xxx read only

11g以前，当需要设置一个表只读时，我们通过赋予某些用户select权限。但对于表的owner来说，还是可以读写的。

从Oracle 11g开始，我们可以通过一下命令设置表只读或可读可写：
alter table tab1 read only;
alter table tab1 read write;

SQL> create table t1 (t number);

Table created

--设置表为只读
SQL> alter table t1 read only;

Table altered

--DML操作，insert/update/delete都不允许
SQL> insert into t1 values (1);

insert into t1 values (1)

ORA-12081: update operation not allowed on table "TOUGH"."T1"

SQL> update t1 set t=0;

update t1 set t=0

ORA-12081: update operation not allowed on table "TOUGH"."T1"

SQL> delete from t1;

delete from t1

ORA-12081: update operation not allowed on table "TOUGH"."T1"

--DDL操作，truncate不允许
SQL> truncate table t1;

truncate table t1

ORA-12081: update operation not allowed on table "TOUGH"."T1"

SQL> alter table t1 add (a number);

alter table t1 add (a number)

ORA-12081: update operation not allowed on table "TOUGH"."T1"

--虽然表设置成了只读，但此处对表进行与索引相关操作，因为索引修改的是数据字典，和表不相关，所以可以进行
SQL> create index t1_indx on t1(t);

Index created

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