Tera-Tom Genius Series - DB2 SQL

Tom Coffing, Leslie Nolander

• Editore: Coffing Publishing
• Anno: 2015
• ISBN:
  9781940540368
• Argomento: Informatik
• Categoria: Data-Warehousing

One of the most popular databases in the world is IBM's DB2. This book has over 600 pages of SQL examples and explanations. This book is a must have for anyone who develops or writes SQL for an IBM DB2 system. Readers will also understand how to create tables, views and indexes. The Authors Tera-Tom Coffing, who has written over 75 successful books on Data Warehousing and Leslie Nolander, Chief Operations Officer (COO) of Coffing Data Warehousing bring a combined 40 years of experience of data warehouse knowledge to create this must have book.

Chapter 1 – The Basics of SQL

“As I would not be a slave, so I would not be a master.”

- Abraham Lincoln

Introduction

The Student_Table above will be used

in our early SQL Examples

This is a pictorial of the Student_Table which we will use to present some basic examples of SQL and get some hands-on experience with querying this table. This book attempts to show you the table, the query, and the result set.

Finding Your Current Schema

The example above shows you how to find your current schema.

Setting Your Default SCHEMA

DB2 allows you do set your default database. Above, we have set our default database to SQL_Class. If we run a query without specifying the database, then DB2 will assume the database is SQL_Class. DB2 refers to this as a schema.

SELECT * (All Columns) in a Table

Most every SQL statement will consist of a SELECT and a FROM. You SELECT the columns you want to see on your report and an Asterisk (*) means you want to see all columns in the table on the returning answer set!

SELECT Specific Columns in a Table

SELECT First_Name

,Last_Name

,Class_Code

,Grade_Pt

FROM Student_Table ;

This is a great way to show the columns you are selecting from the Table_Name.

Commas in the Front or Back?

Why is the example on the left better even though they are functionally equivalent? Errors are easier to spot and comments won’t cause errors.

Place your Commas in front for better Debugging Capabilities

"A life filled with love may have some thorns,
but a life empty of love will have no roses."

Anonymous

Having commas in front to separate column names makes it easier to debug. Remember our quote above. "A query filled with commas at the end just might fill you with thorns, but a query filled with commas in the front will allow you to always come up smelling like roses."

Sort the Data with the ORDER BY Keyword

Rows typically come back to the report in random order. To order the result set, you must use an ORDER BY. When you order by a column, it will order in ASCENDING order. This is called the Major Sort!

ORDER BY Defaults to Ascending

Rows typically come back to the report in random order, but we decided to use the ORDER BY statement. Now, the data comes back ordered by Last_Name.

Use the Name or the Number in your ORDER BY Statement

The ORDER BY can use a number to represent the sort column. The number 2 represents the second column on the report.

Two Examples of ORDER BY using Different Techniques

Notice that the answer set is sorted i...