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    有朋友在ITPUB上提问，如何查询Oracle各组件的版本信息。

其实这个问题，最好的方法是用opatch工具，可以查询得到详细的安装组件版本。
这个可以参考我的网站链接:
http://www.eygle.com/internal/Use.Opatch.apply.Interim.Patch.htm

这里想说说其他的几个视图。有朋友提到了v$version 和 product_component_version 两个视图。
我们来看一下这两者有意思的关系.

首先看看两者的输出:

SQL> select * from PRODUCT_COMPONENT_VERSION;

PRODUCT VERSION STATUS
------------------------------ -------------------- ----------
NLSRTL 9.2.0.4.0 Production
Oracle9i Enterprise Edition 9.2.0.4.0 Production
PL/SQL 9.2.0.4.0 Production
TNS for Linux: 9.2.0.4.0 Production

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
PL/SQL Release 9.2.0.4.0 - Production
CORE 9.2.0.3.0 Production
TNS for Linux: Version 9.2.0.4.0 - Production
NLSRTL Version 9.2.0.4.0 - Production

似乎不同，是么？
那我们再来看看这两者的来源，可以借用一下sqlplus的autotrace功能:

SQL> set autotrace trace explain
SQL> select * from v$version;

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 FIXED TABLE (FULL) OF 'X$VERSION'

SQL> select * from PRODUCT_COMPONENT_VERSION;

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 VIEW OF 'PRODUCT_COMPONENT_VERSION'
2 1 SORT (UNIQUE)
3 2 UNION-ALL
4 3 FIXED TABLE (FULL) OF 'X$VERSION'
5 3 FIXED TABLE (FULL) OF 'X$VERSION'

我们可以发现，这两者都来自底层表x$version，也就是说这两个视图同源，只不过展现有所不同而已。

查询一下x$version的基本信息:

SQL> col indx for 9999
SQL> col inst_id for 99
SQL> select * from x$version;

ADDR INDX INST_ID BANNER
-------- ----- ------- ----------------------------------------------------------------
B701CDCC 0 1 Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
B701CDCC 1 1 PL/SQL Release 9.2.0.4.0 - Production
B701CDCC 2 1 CORE 9.2.0.3.0 Production
B701CDCC 3 1 TNS for Linux: Version 9.2.0.4.0 - Production
B701CDCC 4 1 NLSRTL Version 9.2.0.4.0 - Production

v$version显然是较为单纯的View，那么PRODUCT_COMPONENT_VERSION经过怎样的处理呢？
我们看一下这个视图的创建语句，学习一下Oracle的SQL技术：

CREATE OR REPLACE VIEW SYS.product_component_version (product, VERSION,
status)
AS
(SELECT SUBSTR (banner, 1, INSTR (banner, 'Version') - 1),
SUBSTR (banner,
INSTR (banner, 'Version') + 8,
INSTR (banner, ' - ') - (INSTR (banner, 'Version') + 8)
),
SUBSTR (banner, INSTR (banner, ' - ') + 3)
FROM v$version
WHERE INSTR (banner, 'Version') > 0
AND ( (INSTR (banner, 'Version') < INSTR (banner, 'Release'))
OR INSTR (banner, 'Release') = 0
))
UNION
(SELECT SUBSTR (banner, 1, INSTR (banner, 'Release') - 1),
SUBSTR (banner,
INSTR (banner, 'Release') + 8,
INSTR (banner, ' - ') - (INSTR (banner, 'Release') + 8)
),
SUBSTR (banner, INSTR (banner, ' - ') + 3)
FROM v$version
WHERE INSTR (banner, 'Release') > 0
AND INSTR (banner, 'Release') < INSTR (banner, ' - '))

很多东西只要深入一点点，就能发现问题的本质。
是不是很好玩呢?

-The End-