Oracle虚拟列

创建带虚拟列的表

create table t_vir_col
(
empno number,
name varchar2(100),
birth date,
birthmonth varchar2(3) GENERATED ALWAYS AS (to_char(birth,'mm')) VIRTUAL,
age number GENERATED ALWAYS AS (floor(months_between(sysdate,birth)/12)) VIRTUAL
);

报错,因为使用了sysdate，这个值返回的数据不确定，所以没法使用。

ERROR at line 7:
ORA-54002: only pure functions can be specified in a virtual column expression

改用确定值：

create table t_vir_col_2
(
empno number,
name varchar2(100),
birth date,
birthmonth varchar2(3) GENERATED ALWAYS AS (to_char(birth,'mm')) VIRTUAL,
age number GENERATED ALWAYS AS (floor(months_between(to_date('2018-12-31','yyyy-mm-dd'),birth)/12)) VIRTUAL
);

创建成功。

去掉 age 列：

create table t_vir_col
(
empno number,
name varchar2(100),
birth date,
birthmonth varchar2(3) GENERATED ALWAYS AS (to_char(birth,'mm')) VIRTUAL
);
Table created.

SQL> 

插入数据

insert into t_vir_col (empno,name,birth)  values(1,'a',to_date('1999-10-10','yyyy-mm-dd'));

查询数据：

SQL> select * from t_vir_col;

     EMPNO NAME                 BIRTH     BIRTHMONTH
---------- -------------------- --------- --------------------
         1 a                    10-OCT-99 10

SQL> 

虚拟列分区

drop table t_vir_col;
create table t_vir_col
(
empno number,
name varchar2(100),
birth date,
birthmonth number GENERATED ALWAYS AS (to_number(to_char(birth,'mm'))) VIRTUAL
) 
partition by range (birthmonth)
(
partition month_01 values less than (2),
partition month_02 values less than (3),
partition month_03 values less than (4),
partition month_04 values less than (5),
partition month_05 values less than (6),
partition month_06 values less than (7),
partition month_07 values less than (8),
partition month_08 values less than (9),
partition month_09 values less than (10),
partition month_10 values less than (11),
partition month_11 values less than (12),
partition month_12 values less than (13)
);

创建成功。

分区列不能更新：

SQL> update t_vir_col set  birth=to_date('1999-11-10','yyyy-mm-dd') where empno=1;
update t_vir_col set  birth=to_date('1999-11-10','yyyy-mm-dd') where empno=1
       *
ERROR at line 1:
ORA-14402: updating partition key column would cause a partition change

SQL> update t_vir_col set  birth=to_date('1998-10-10','yyyy-mm-dd') where empno=1;

1 row updated.

虚拟列也不能更新：

SQL> update t_vir_col_2 set age=20 where empno=1;
update t_vir_col_2 set age=20 where empno=1
       *
ERROR at line 1:
ORA-54017: UPDATE operation disallowed on virtual columns

参考链接：
http://blog.51cto.com/tiany/1570419