标签：oracle
Oracle 11g新特性之--虚拟列（Virtual Column)
Oracle 11G虚拟列Virtual Column介绍
Oracle 11G 在表中引入了虚拟列，虚拟列是一个表达式，在运行时计算，不存储在数据库中，不能更新虚拟列的值。
定义一个虚拟列的语法：
column_name [datatype] [GENERATED ALWAYS] AS [expression] [VIRTUAL]
1.虚拟列可以用在select，update，delete语句的where条件中，但是不能用于DML语句
2.可以基于虚拟列来做分区
3. 可以在虚拟列上建索引，oracle的函数索引就类似。
4. 可以在虚拟列上建约束
案例：
1、创建一个带虚拟列的表：
14:51:28 SCOTT@ test1 >CREATE TABLE EMP3 14:51:51 2 ( 14:51:51 3 EMPNO NUMBER(6), 14:51:51 4 SAL NUMBER(8,2), 14:51:51 5 COMM NUMBER(8,2), 14:51:51 6 SAL_PACK GENERATED ALWAYS AS ( SAL + NVL(COMM,0) ) VIRTUAL 14:51:51 7 ) Table created.
2、查看虚拟列属性
14:56:10 SCOTT@ test1 >COL TABLE_NAME FOR A10
14:56:19 SCOTT@ test1 >COL COLUMN_NAME FOR A20
14:56:27 SCOTT@ test1 >COL DATA_TYPE FOR A20
14:56:34 SCOTT@ test1 >COL DATA_DEFAULT FOR A20
14:56:48 SCOTT@ test1 >R
1 select table_name,COLUMN_NAME,data_type,data_default,VIRTUAL_COLUMN from user_tab_cols
2* where table_name=‘EMP3‘
TABLE_NAME COLUMN_NAME DATA_TYPE DATA_DEFAULT VIR
---------- -------------------- -------------------- -------------------- ---
EMP3 SAL_PACK NUMBER "SAL"+NVL("COMM",0) YES
EMP3 COMM NUMBER NO
EMP3 SAL NUMBER NO
EMP3 EMPNO NUMBER NO 上述建的虚拟列 SAL_PACK 是由一个简单的表达式创建的，使用的关键字有 VIRTUAL（不过这个关键字是可选的），该字段的值是由 COMM 这个字段通过表达式计算而来的。
在Table上添加虚拟列:
15:44:12 SCOTT@ test1 >alter table emp3 add (sal_total as (sal*12+comm) virtual);
Table altered.
15:49:11 SCOTT@ test1 >desc emp3;
Name Null? Type
----------------------------------------------------------------- -------- --------------------------------------------
EMPNO NUMBER(6)
SAL NUMBER(8,2)
COMM NUMBER(8,2)
SAL_PACK NOT NULL NUMBER
SAL_TOTAL NUMBER
15:49:16 SCOTT@ test1 >select * from emp3;
EMPNO SAL COMM SAL_PACK SAL_TOTAL
---------- ---------- ---------- ---------- ----------
10 1500 500 2000 18500
20 3000 500 3500 36500
30 4000 500 4500 48500
40 6000 500 6500 72500
15:51:00 SCOTT@ test1 >select table_name,COLUMN_NAME,data_type,data_default,VIRTUAL_COLUMN from user_tab_cols
15:51:27 2 where table_name=‘EMP3‘;
TABLE_NAME COLUMN_NAME DATA_TYPE DATA_DEFAULT VIR
---------- -------------------- -------------------- -------------------- ---
EMP3 SAL_TOTAL NUMBER "SAL"*12+"COMM" YES
EMP3 SAL_PACK NUMBER "SAL"+NVL("COMM",0) YES
EMP3 COMM NUMBER NO
EMP3 SAL NUMBER NO
EMP3 EMPNO NUMBER NO在虚拟列中使用函数：
15:51:37 SCOTT@ test1 >CREATE OR REPLACE FUNCTION sum_sal (in_num1 NUMBER, in_num2 NUMBER) 15:57:17 2 RETURN NUMBER DETERMINISTIC 15:57:17 3 AS 15:57:17 4 BEGIN 15:57:17 5 RETURN in_num1 + in_num2; 15:57:18 6 END; 15:57:19 7 / Function created. 15:57:21 SCOTT@ test1 >alter table emp3 add ( sal_comm as (sum_sal(sal,comm)) virtual); Table altered. 16:00:03 SCOTT@ test1 >desc emp3 Name Null? Type ----------------------------------------------------------------- -------- -------------------------------------------- EMPNO NUMBER(6) SAL NUMBER(8,2) COMM NUMBER(8,2) SAL_PACK NOT NULL NUMBER SAL_TOTAL NUMBER SAL_COMM NUMBER 16:00:07 SCOTT@ test1 >select * from emp3; EMPNO SAL COMM SAL_PACK SAL_TOTAL SAL_COMM ---------- ---------- ---------- ---------- ---------- ---------- 10 1500 500 2000 18500 2000 20 3000 500 3500 36500 3500 30 4000 500 4500 48500 4500 40 6000 500 6500 72500 6500
虚拟列的值是不存储在磁盘的，它们是在查询时根据定义的表达式临时计算的。
3、对虚拟列的操作
Insert 操作：
我们不能往虚拟列中插入数据： 15:01:52 SCOTT@ test1 >insert into emp3 values (10,1500,500,2000); insert into emp3 values (10,1500,500,2000) * ERROR at line 1: ORA-54013: INSERT operation disallowed on virtual columns 也不能隐式的添加数据到虚拟列： 15:02:16 SCOTT@ test1 >insert into emp3 values (10,1500,500); insert into emp3 values (10,1500,500) * ERROR at line 1: ORA-00947: not enough values 虚拟列的数据会自动计算生成 15:07:16 SCOTT@ test1 >insert into emp3(empno,sal,comm) values (10,1500,500); 1 row created. 15:07:29 SCOTT@ test1 >select * from emp3; EMPNO SAL COMM SAL_PACK ---------- ---------- ---------- ---------- 10 1500 500 2000
对虚拟列不能做update操作：
15:18:45 SCOTT@ test1 >update emp3 set sal_pack=3000; update emp3 set sal_pack=3000 * ERROR at line 1: ORA-54017: UPDATE operation disallowed on virtual columns
在虚拟列上创建索引和约束：
15:19:07 SCOTT@ test1 >create index emp3_val_ind on emp3(sal_pack) tablespace indx; Index created. 15:21:20 SCOTT@ test1 >select table_name,index_name,INDEX_TYPE from user_indexes 15:22:11 2 where table_name=‘EMP3‘; TABLE_NAME INDEX_NAME INDEX_TYPE ---------- ------------------------------ --------------------------- EMP3 EMP3_VAL_IND FUNCTION-BASED NORMAL 15:22:18 SCOTT@ test1 >drop index EMP3_VAL_IND; Index dropped. 15:24:37 SCOTT@ test1 >alter table emp3 add constraint pk_emp3 primary key (sal_pack); Table altered. 15:25:22 SCOTT@ test1 >select table_name,index_name,INDEX_TYPE from user_indexes 15:25:34 2 where table_name=‘EMP3‘; TABLE_NAME INDEX_NAME INDEX_TYPE ---------- ------------------------------ --------------------------- EMP3 PK_EMP3 FUNCTION-BASED NORMAL
在虚拟列上建立分区表:
15:41:43 SCOTT@ test1 >CREATE TABLE EMP3_part 15:41:46 2 ( 15:41:46 3 EMPNO NUMBER(6), 15:41:46 4 SAL NUMBER(8,2), 15:41:46 5 COMM NUMBER(8,2), 15:41:46 6 SAL_PACK GENERATED ALWAYS AS ( SAL + NVL(COMM,0) ) VIRTUAL 15:41:46 7 ) 15:41:46 8 PARTITION BY range (sal_pack) 15:41:46 9 (PARTITION sal_2000 VALUES LESS THAN (2000), 15:41:46 10 PARTITION sal_4000 VALUES LESS THAN (4000), 15:41:46 11 PARTITION sal_6000 VALUES LESS THAN (6000), 15:41:46 12 PARTITION sal_8000 VALUES LESS THAN (8000), 15:41:46 13 PARTITION sal_default VALUES LESS THAN (MAXVALUE)); Table created. 15:42:33 SCOTT@ test1 >insert into emp3_part(empno,sal,comm) select empno,sal,comm from emp3; 4 rows created. 15:43:33 SCOTT@ test1 >commit; Commit complete. 15:43:36 SCOTT@ test1 >select * from emp3_part; EMPNO SAL COMM SAL_PACK ---------- ---------- ---------- ---------- 10 1500 500 2000 20 3000 500 3500 30 4000 500 4500 40 6000 500 6500 15:43:44 SCOTT@ test1 >select * from emp3_part partition(sal_2000); no rows selected 15:44:01 SCOTT@ test1 >select * from emp3_part partition(sal_4000); EMPNO SAL COMM SAL_PACK ---------- ---------- ---------- ---------- 10 1500 500 2000 20 3000 500 3500
本文出自 “天涯客的blog” 博客，请务必保留此出处http://tiany.blog.51cto.com/513694/1570419
Oracle 11g新特性之--虚拟列（Virtual Column)
标签：oracle
原文地址：http://tiany.blog.51cto.com/513694/1570419
