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SQL and XQuery tutorial for IBM DB2, Part 2: Basic queries

The fundamentals of SQL queries

Pat Moffatt (pmoffatt@ca.ibm.com), Information Management Program Manager, IBM Academic Initiative, IBM
Pat Moffatt is the Information Management Program Manager for the IBM Academic Initiative. Through the Academic Initiative program, she ensures that appropriate Information Management resources are made available to help faculty integrate Information Management software into their curriculum. To learn more about this program, visit www.ibm.com/university/data.
Bruce Creighton (bcreight@ca.ibm.com), Skills Segment Planner, IBM
Bruce Creighton is a Skills Segment Planner in the Information Management Education Planning and Development department. In this role, he plans investment in educational content and balances the investment between areas where IBM can attain revenue and those where the requirement for skills development are important enough to provide free education.
Jessica Cao, Training Tools Developer, IBM
Jessica Cao is an Arts and Science and Computer Science student at McMaster University. She expects to complete her combined honours degree in April 2009. Jessica is working in IBM Toronto lab's DB2 Information Management Skills Channel Planning and Enablement Program to take advantage of her interest in programming, editing, and writing.

Summary:  Through a series of simple examples, this tutorial illustrates how to retrieve data from an IBM® DB2® database with standard SQL SELECT statements. This tutorial describes how to retrieve rows from a relational database table, retrieve specific columns, retrieve specific rows, reform logical operations on retrieved data, and use wildcard characters in search conditions. This tutorial is Part 2 of the SQL & XQuery tutorial for IBM DB2 series.

View more content in this series

Date:  03 Aug 2006
Level:  Introductory PDF:  A4 and Letter (97 KB | 25 pages)Get Adobe® Reader®

Activity:  39943 views
Comments:  

Naming columns using the AS clause

Question

Which cities are in districts that begin with the letters Min? Name the hq_city column to make more sense.

Example query

		SELECT district, hq_city AS City
		FROM aroma.market
		WHERE district LIKE 'Min%';

Result

DistrictCity
MinneapolisMinneapolis
MinneapolisMilwaukee

Naming expressions: AS

The optional AS clause lets you assign a meaningful name to an expression, which makes referring back to the expression easier. When using the AS clause, there are rules on allowable names. In general, valid names must begin with a letter, be no longer than 128 characters, have no blank spaces, and cannot be a SQL keyword. An SQL keyword would be SELECT, FROM, WHERE, and etc. For more detail on SQL keywords, refer to the SQL Reference Guide .

For example, the following AS clause assigns the alias hq_city to the City column:

       hq_city AS City

You can assign the alias without using the keyword AS, but it may not be as obvious when you look at your query:

       hq_city City

You will note that regardless of capitalization in the expression, column headers are displayed in all uppercase.

About the query

The example query returns the same result set as the previous query in this chapter; however, in this case, column aliases are assigned to create headings for the aggregated results.

arrow Important: If the value contained in the column referenced by the column alias is the result of a set function, it cannot occur in the WHERE clause; however, it can occur in the HAVING clause. For more information on the HAVING clause, see Part 4 of this series.

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