Book Image

Oracle Database 11gR2 Performance Tuning Cookbook

By : Ciro Fiorillo
Book Image

Oracle Database 11gR2 Performance Tuning Cookbook

By: Ciro Fiorillo

Overview of this book

Oracle's Database offers great performance, scalability, and many features for DBAs and developers. Due to a wide choice of technologies, successful applications are good candidates to run into performance issues and when a problem arises it's very difficult to identify the cause and the right solution to the problem. The Oracle Database 11g R2 Performance Tuning Cookbook helps DBAs and developers to understand every aspect of Oracle Database that can affect performance. You will be guided through implementing the correct solution in a proactive way before problems arise, and how to diagnose issues on your Oracle database-based solutions. This fast-paced book offers solutions starting from application design and development, through the implementation of well-performing applications, to the details of deployment and delivering best-performance databases. With this book you will quickly learn to apply the right methodology to tune the performance of an Oracle Database, and to optimize application design and SQL and PL/SQL code. By following the real-world examples you will see how to store your data in correct structures and access and manipulate them at a lightning speed. You will learn to speed up sort operations, hack the optimizer and the data loading process, and diagnose and tune memory, I/O, and contention issues. The purpose of this cookbook is to provide concise recipes, which will help you to build and maintain a very high-speed Oracle Database environment.
Table of Contents (21 chapters)
Oracle Database 11gR2 Performance Tuning Cookbook
Credits
About the Author
Acknowledgement
About the Reviewers
www.PacktPub.com
Preface
Index

Writing top n queries and ranking


One common problem when developing database applications is to show the first n rows of a set, ordering the data in a specific manner. For example, if we want to see the last 10 articles submitted in a web application.

In this recipe, we will see how to obtain this scope and how to obtain it faster.

How to do it...

The following steps will demonstrate how to get the top n queries and their ranking:

  1. Connect to the SH schema:

    CONNECT sh@TESTDB/sh
    
  2. Select the first 10 customers, ordered by their age, from youngest to oldest:

    SELECT CUST_ID, CUST_FIRST_NAME, CUST_LAST_NAME, CUST_YEAR_OF_BIRTH
    FROM CUSTOMERS
    WHERE ROWNUM < 11
    ORDER BY CUST_YEAR_OF_BIRTH DESC;
    
  3. The correct way to express the previously selected statement is:

    SELECT * FROM (
      SELECT CUST_ID, CUST_FIRST_NAME, CUST_LAST_NAME, CUST_YEAR_OF_BIRTH
      FROM CUSTOMERS
      ORDER BY CUST_YEAR_OF_BIRTH DESC
    )
    WHERE ROWNUM < 11;
    
  4. Using the RANK() function may lead to different results:

    SELECT * FROM (
      SELECT...