I came across one strange issue today (actually I found this last Friday, but you know weekend coming, hehehe).

When using the update DQL to fill up one new column in the registered table, there are always lots of blanks appended.

The root cause after doing some investigation, what I found:

We are adding the column in type – char rather than varchar2 which is the normal one.

CHAR should be used for storing fix length character strings. String values will be space/blank padded before stored on disk.

Baiqing, one of my colleges , wrote the DQL to add the new column. I believe that:

1. He should be more careful

2. The DQL used to register table in Documentum are defining the type as ‘char’. Documentum is using ‘char’ type to define variable length character strings. there is no type to define fix length strings. That make developer confused.

Anyway, the cause was found. Happy Monday!!!!

Reference:

http://www.orafaq.com/faq/what_is_the_difference_between_varchar_varchar2_and_char_data_types

You can follow this article step by step:

http://www.itpub.net/viewthread.php?tid=806933&extra=&page=1

Note:

1. I was installing oracle in RedHat Enterprise Linux 4 Update 3, the only missing package is gcc.You can get help from this page:

http://hi.baidu.com/thinkinginlamp/blog/item/f91ad1138ac429025aaf53e2.html

1. If you are installing oracle in linux OS which doesn’t have language Chinese installed, then you should not set environment variable NLS_LANG mentioned in the above article.
2. After update oracle to 10.2.0.3, you should run the following sql statements to upgrade data dictionary: (go to folder ORACLE_HOME, then startup sqlplus)

SQL> STARTUP UPGRADE
$K”qE5x[1]e.gd’rO0SQL> @?\rdbms\admin\catupgrd.sql

SQL>@?\rdbms\admin\utlrp.sqlITPUB个人空间F/`Q Q.qu7yqOITPUB个人空间i5y(D*zT’?

Install Documentum Content server 6.5

The main resource is ContentServerInstallGuide_6.5.pdf.

1. Follow chapter Required Environment Variables for UNIX and Linux and chapter Preparing the Database for Content Server Installation to set all required environment variables.
2. Copy files tnsnamse.ora and listener.ora from $ORACLE_HOME/network/admin to $TNS_ADMIN
3. Follow chapter Installing content Server to install content server and create docbase and docbroker.

Appendix A: How to start/stop oracle:

http://hua6884858.javaeye.com/blog/441251

Appendix B: How to start/stop docbase/docbroker:

All the shell file is located in $DOCUMENTUM/dba

Such as dm_launch_<Docbroker-name>, dm_stop_<Docbroker-name>, dm_start_<Dobase-name>, dm_shutdown_<Docbase-name>

1. spool命令

1 Oracle的spool命令可以用来将数据export出来到文本文件。Oracle的Import/Export命令用于备份和恢复比较有效，但对于一些临时数据量的导出，Export不好用，甚至不可用。在这里，就是spool的发挥之地了。

2Spool一般使用格式为spool [filepath]filename;       其他sql语句；spool off;

要输出的内容都在spool语句中包含；

3 spool还有些其他控制命令：

set pagesize 0               –设置页面大小， 0表示无限制，如果设置为10,则10行数据后出现一空行
set num 18                  –设置数字的长度，如果不够大，则用科学记数法显示
set heading off             –设置不要题头，则不出现select的field list
set feedback off           –设置不需要返回信息， 比如” 100 rows selected“
set term off                 –
set trimspool on           –trim

4 如果在sqlplus中直接使用sql语句，则导出的数据文件中会包含spool语句中使用的sql语句，如果不想让生成这些可把要使用的sql语句存在一个文件中再在sqlplus中执行此文件即可。

1. 使用select语句批量拼装sql语句

仿照select ‘insert into table_name values(”’||field_1||”’,”’||field_2||”’);’from table_name where field_n=some_conditon;可联想批量生成其他sql语句，例如drop、update、delete语句。其中||为连接符号，三个单引号最后生成一个单引号。

After you have created a database link, you can use it to refer to tables and views on the other database. In SQL statements, you can refer to a table or view on the other database by appending @dblink to the table or view name. You can query a table or view on the other database with the SELECT statement. You can also access remote tables and views using any INSERT, UPDATE, DELETE, or LOCK TABLE statement.

There are two kinds of timezone:

1. DBTIMEZONE you can set the time zone for database by “alter database set time_zone=’+08:00′”. To make
this take effect, you should reboot the database. But if you have a column that is of TIMESTAMP WITH TIME ZONE/LOCAL TIME ZONE, you will not be able to change the DBTIMEZONE. SYSTIMESTAMP is used to get the current database timestamp with time zone information. BTW, SYSDATE is used to get the current date without time zone information.

2. SESSIONTIMEZONE you can set time zone at the session level
e.g. you can issue “alter session set TIME_ZONE=’+08::00′;” to change the timezone for current session. CURRENT_TIMESTAMP is used to get the current session timestamp with time zone infomation.

There are three types of timestamp:

1. timestamp

2. timestamp with time zone

3. timestamp with local time zone

The key point is “The main idea to grasp here is that the column with datatype TIMESTAMP WITH TIME ZONE stores and displays the explicit time supplied from the INSERT statement. The column with datatype TIMESTAMP WITH LOCAL TIME ZONE stores the explicit time supplied but will display a value that is relative to the current session time zone. This means that if you want hard and fast TIMESTAMPS with time zone information stored, you should use the TIMESTAMP WITH TIME ZONE datatype. If you are concerned more with giving date and time information to customers in different time zones and represented in their local time, you should use the TIMESTAMP WITH LOCAL TIME ZONE datatype.”

references:

http://www.dbasupport.com/oracle/ora9i/TimeZone.shtml

http://toolkit.rdbms-insight.com/tz.php

P.S. you can get all valid timezone name by “select tzname, tzabbrev from V$TIMEZONE_NAMES”

Select * from T1 where x in ( select y from T2 )

is typically processed as:

select *
from t1, ( select distinct y from t2 ) t2
where t1.x = t2.y;

The subquery is evaluated, distinct’ed, indexed (or hashed or sorted) and then joined to
the original table — typically.

As opposed to

select * from t1 where exists ( select null from t2 where y = x )

That is processed more like:

for x in ( select * from t1 )
loop
if ( exists ( select null from t2 where y = x.x )
then
OUTPUT THE RECORD
end if
end loop

It always results in a full scan of T1 whereas the first query can make use of an index
on T1(x).

So, when is where exists appropriate and in appropriate?

Lets say the result of the subquery
( select y from T2 )

is “huge” and takes a long time.  But the table T1 is relatively small and executing (
select null from t2 where y = x.x ) is very very fast (nice index on t2(y)).  Then the
exists will be faster as the time to full scan T1 and do the index probe into T2 could be
less then the time to simply full scan T2 to build the subquery we need to distinct on.

Lets say the result of the subquery is small — then IN is typicaly more appropriate.

If both the subquery and the outer table are huge — either might work as well as the
other — depends on the indexes and other factors.

This is from:

http://asktom.oracle.com

FOR record_index in cursor_name
LOOP
{.statements.}
END LOOP;

You would use a CURSOR FOR Loop when you want to fetch and process every record in a cursor. The CURSOR FOR Loop will terminate when all of the records in the cursor have been fetched.

Here is an example of a function that uses a CURSOR FOR Loop:

CREATE OR REPLACE Function TotalIncome
( name_in IN varchar2 )
RETURN varchar2
IS
total_val number(6);
cursor c1 is
select monthly_income
from employees
where name = name_in;
BEGIN
total_val := 0;
FOR employee_rec in c1
LOOP
total_val := total_val + employee_rec.monthly_income;
END LOOP;
RETURN total_val;
END;

In this example, we’ve created a cursor called c1. The CURSOR FOR Loop will terminate after all records have been fetched from the cursor c1.

The keyword SNAPSHOT is supported in place of MATERIALIZED VIEW for backward compatibility.

Prerequisites

The materialized view must be in your own schema or you must have the DROP ANY MATERIALIZED VIEW system privilege. You must also have the privileges to drop the internal table, views, and index that the database uses to maintain the materialized view data.