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SQL & PL/SQL

SQL and PL/SQL Articles

Diff B/W Truncate & Delete

Delete
1.DML data can be recovered by rollback before commit
2.Remove any subset of data
3.Delete is slower when table have numerous indexes and triggers
4.DML triggers fire for delete mthod
5.data can be recovered after commit by flashback method
6.high water mark will remain the same
7.data deleted info capture with returning clause
8. you can not delete data if function based index is invalid
9. can not delete data from complex views.
10.

What data type should I use: CHAR or VARCHAR2???

Hi,

We all know that CHAR and VARCHAR2 are two different datatypes used for storing strings in Oracle. When I asked many people about what’s the difference exactly, all were saying VARCHAR2 can be used for variable sized character strings. As I’m not satesfied with the answer, as always, I’ve decided to do my own experiments on these two.

Please use ANSI join syntax

The old Oracle join syntax really should be consigned to history.

Script to find Oracle database performance

This single script provides the overall picture of the database in terms of Waits events, Active/Inactive killed sessions, Top Processes (physical I/O, logical I/O, memory and CPU processes), Top CPU usage by users, etc.

[code]set serveroutput on
declare
cursor c1 is select version
from v$instance;
cursor c2 is
select
host_name
, instance_name
, to_char(sysdate, 'HH24:MI:SS DD-MON-YY') currtime
, to_char(startup_time, 'HH24:MI:SS DD-MON-YY') starttime
from v$instance;
cursor c4 is
select * from (SELECT count(*) cnt, substr(event,1,50)

DBMS_FGA - Oracle Fine Grained Auditing

dwaipayan1986's picture

Suppose your boss calls you one day and tells you that there has been some unexpected changes in the employee database.Employee's designation, their salary are being manipulated illegally.Such things have been continuing from a past few days and he asks if you could help getting hold of the culprit.
Don't worry Oracle's DBMS_FGA package will save your day and earn you a raise in your job.

The Oracle DBMS_FGA package provides fine grained auditing on objects.

To have an overview of the summary of dbms_fga subprograms visit :

»

8 Bulk Update Methods Compared

What I love about writing SQL Tuning articles is that I very rarely end up publishing the findings I set out to achieve. With this one, I set out to demonstrate the advantages of PARALLEL DML, didn't find what I thought I would, and ended up testing 8 different techniques to find out how they differed. And guess what? I still didn't get the results I expected. Hey, at least I learned something.

As an ETL designer, I hate updates. They are just plain nasty. I spend an inordinate proportion of design time of an ETL system worrying about the relative proportion of rows inserted vs updated. I worry about how ETL tools apply updates (did you know DataStage applys updates singly, but batches inserts in arrays?), how I might cluster rows together that are subject to updates, and what I might do if I just get too many updates to handle.

It would be fair to say I obsess about them. A little bit.

Oracle Rules Manager by example

shouvikb's picture

Simple introduction to Oracle Database 11g Rules Manager using good old EMP table.

This Article introduces Oracle Rules Manager in a series of simple examples with imaginary cases on the EMP table. This article is an overview of the possibilities of Oracle Rule Manager for a traditional Oracle Architect who has never thought of a Rule based approach. It will also be informative to communities working actively with other Rule Engines, who never considered the Oracle Rule Manager.

Tuning Goldilocks SQL

Tuning Goldilocks SQL

... then Goldilocks went into the bears' Data Centre and there were 3 Oracle databases. The first was a Data Warehouse. Goldilocks checked the AWR, but all the SQLs were to-o-o-o-o-o-o-o big; they all used full scans, hash joins, bitmap-index combining, partition pruning and parallelism and couldn't be tuned any more. So Goldilocks went to the second Oracle database. It was an OLTP system with hundreds of concurrent users. Goldilocks fired up SQL Tuning Advisor, but all the SQLs were to-o-o-o-o-o-o-o small; they used unique index scans and cluster-joins and couldn't be tuned any more. So Goldilocks went to the third Oracle database. It was an Operational Data Store with a rolling 3 month retention. Goldilocks found SQLs that were joining a million rows with Nested Loops joins, buffer cache hit ratios of 50%, and under-utilised disk. She smiled, opened up Tom Kyte's Expert Oracle eBook on her second monitor and got to work. This database was ju-u-u-u-u-u-u-u-st right ...

Word-Based Password Generator

During my experiences with different environments, I have been tasked with maintaining passwords for different information systems. This includes operating system accounts (root, oracle, administrator) and Database accounts (sys, system, dbsnmp).

It can be sometimes difficult to remember many different passwords. I have seen some people overcome this by documenting the passwords, sometimes just in a plaintext file, sometimes encrypted, sometimes just on a ‘Post-It’ Note under the keyboard.

I try and retain the passwords in memory.

Using Regular Expressions in Oracle

Everyday most of us deal with multiple string functions in Sql. May it be for truncating a string, searching for a substring or locating the presence of special characters.

The regexp functions available in Oracle 10g can help us achieve the above tasks in a simpler and faster way.