 | Level: Introductory Pat Moffatt (pmoffatt@ca.ibm.com), Information Management Program Manager, IBM Academic Initiative, IBM
Bruce Creighton (bcreight@ca.ibm.com), Skills Segment Planner, IBM
Jessica Cao , Training Tools Developer, IBM
24 Aug 2006 This tutorial describes queries that compare data in an IBM® DB2® database. This is accomplished by using either CASE expressions or subqueries. This tutorial is Part 5 of the SQL & XQuery tutorial for IBM DB2 series.
Prerequisites
This tutorial was written for DB2 Express-C 9 for UNIX®, Linux® and Windows® (formerly known as Viper). You should be familiar with DB2 and databases. It is preferable that you view tutorials one, two, three, and four in this series before attempting this tutorial, part five.
System requirements
To use this tutorial to the fullest, you should have IBM DB2 9 installed. Download DB2 Express-C, a no-charge version of DB2 Express Edition for the community that offers the same core data features as DB2 Express Edtion and provides a solid base to build and deploy applications. You will also need to install the Aroma database, which can be downloaded in the tutorial.
Duration
Under 2 hours
Formats html, pdf
About this tutorial
This tutorial discusses queries that compare data in an IBM DB2 database. It begins by illustrating the problem that confronts the query writer: how to use SQL to return a spreadsheet or "cross-tab" report rather than a standard, vertically ordered result set that is hard to read. The problem is solved by using either CASE expressions or subqueries.
The CASE solution, presented first, is a simple and concise way of comparing similar groups of values. Next, several examples of FROM clause and select-list subqueries are presented. These subqueries have the added value of being able to both compare data from different groups and include calculations against the compared values, such as share percentages over given time periods.
This tutorial describes subqueries stated as conditions in the WHERE clause, which are useful for simpler comparison queries. The last section also describes the ALL, EXISTS, and SOME or ANY predicates, which can be used to express conditions on subquery results.
| | | |
