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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:  

Using the Greater-Than (>) and Less-Than or Equal-To (<=) operators

Question

Which cities and districts are identified by Mktkey values that are greater than 4 and less than or equal to 12?

Example query

		SELECT mktkey, hq_city, hq_state, district
		FROM aroma.market
		WHERE mktkey > 4
			AND mktkey <= 12;

Result

MktkeyHq_CityHq_StateDistrict
5New YorkNYNew York
6PhiladelphiaPANew York
7BostonMABoston
8HartfordCTBoston
9ChicagoILChicago
10DetroitMIChicago
11MinneapolisMNMinneapolis
12MilwaukeeWIMinneapolis

Using comparison operators

Conditions evaluate to true or false and can be expressed with comparison operators or comparison predicates. SQL contains the following comparison operators:

OperatorName
=equal
<less than
>greater than
<>not equal
>=greater than or equal
<=less than or equal

About the query

The example query retrieves and displays all cities and districts whose Mktkey is greater than 4 but less than or equal to 12.

The Mktkey column contains integer values, which are comparable to other numeric values. If you compare an integer to a character, however, the server returns an error message:

        SELECT mktkey, hq_city, hq_state, district
        FROM aroma.market
        WHERE mktkey > '4';
        
        [IBM][CLI Driver][DB2/LINUX] SQL0401N  The data types of the operands 
        for the operation ">" are not compatible.  SQLSTATE=42818

You can obtain help interpreting error messages, and identifying corrective action that can be taken, by using the DB2 Information Center. The Center was introduced in Part 1 of this series.

Usage notes

Conditions must compare values of comparable data types. If you attempt to compare unlike data types, the server returns either an error message or an incorrect result. Comparison operators can be used to compare one character string with another, as the following legal condition illustrates:

(city > 'L')

For more information about comparable data types, refer to the SQL Reference Guide .

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