03
Thu, Oct
2 New Articles

Partner TechTip: Creating SQL Materialized Queries

SQL
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

Despite our best efforts to achieve excellent database normalization, sometimes it's necessary or simply more efficient to create a temporary table containing some data as of a certain time. SQL satisfies this need with Materialized Query Tables (MQT). These specialized SQL objects allow a database administrator to define the data selected for inclusion and then easily refresh the query with current data from the database tables as needed.

The most powerful use of an MQT is not having users access it directly, but allowing the SQL optimizer to choose to use the MQT instead of the underlying base tables to satisfy other SQL statements. Anytime an application needs static data—such as end of year, end of month, or end of day statistics—this information, which might normally be found by accumulating data from detail tables, could instead be provided by creating an MQT that contains this static data.

Creating a Materialized Query

Creating MQTs relies upon the SQL CREATE statement, as shown below:

CREATE TABLE INVTOTALS AS                              
(WITH TEMP AS (SELECT DEC(SUM(QTY),7,0) as TOTAL,      
PART FROM INVDETL                                      
 GROUP BY PART)                                        
SELECT INVMAST.PART, DESC, PRICE, COST, TOTAL FROM INVMAST 
 LEFT JOIN TEMP ON INVMAST.PART = TEMP.PART)           
 DATA INITIALLY DEFERRED                               
 REFRESH DEFERRED    
 ENABLE QUERY OPTIMIZATION                                  
 MAINTAINED BY USER                                    

This statement creates an MQT named INVTOTALS. This query contains the part number, description, price, and cost from the inventory master file joined with the sum of the quantity column for each part. TOTAL is the name assigned to the total quantity. This statement uses WITH to define a temporary table object before resolving the main select. This temporary table, named TEMP, contains only a list of parts from the INVDETL file and the total of the QTY column for each part. Using WITH frequently simplifies the code needed later in the main select. Following the main select are four clauses that further define the MQT.

  • DATA INITIALLY DEFERRED indicates that the MQT is not loaded with data at the time of creation. Use DATA INITIALLY IMMEDIATE to load it with data right away if necessary.
  • REFRESH DEFERRED indicates that the user may choose to refresh the table at any time by issuing the REFRESH TABLE mqt-name statement. This clause is not optional.
  • ENABLE QUERY OPTIMIZATION indicates that the SQL engine may choose to use this MQT to satisfy other SQL statements issued against the underlying table(s). To deactivate this feature, use DISBALE QUERY OPTIMIZATION instead.
  • MAINTAINED BY USER indicates that the user is responsible for loading the correct data into the MQT using INSERT, UPDATE, DELETE, and REFRESH TABLE statements. This is not optional.

Managing Materialized Queries

The data within an MQT is static, meaning that once data is loaded into it, it will not change regardless of what happens to the underlying tables. Programmers may choose to manually update the MQT with INSERT, UPDATE, and DELETE statements, or more likely, they can repopulate the table with current data using the REFRESH TABLE statement such as the one shown below.

REFRESH TABLE INVTOTALS    

QAQQINI File

To enable the use of MQTs within the SQL optimizer, the QAQQINI file must be updated, as the default settings do not allow the use of Materialized Queries during the optimization process. These settings are needed:

MATERIALIZED_QUERY_TABLE_USAGE = *ALL 
MATERIALIZED_QUERY_TABLE_REFRESH_AGE = *ANY  

Want to Know More?

Materialized Queries are a powerful new tool for improving SQL performance within DB2 for i5/OS. This article just touches the tip of the iceberg. For more information on MQTs, check out IBM's white paper "Creating and using materialized query tables (MQT) in IBM DB2 for i5/OS" or contact DMC Consulting about its new "SQL: Data Definition Language" class. This newly created class explores the details of creating DB2 for i5/OS databases through SQL. Contact DMC by email at This email address is being protected from spambots. You need JavaScript enabled to view it. or by phone at 419.535.2900 to either sign up for a class in the open schedule or schedule a private class for your own company. Find out more about DMC Consulting, a Premier IBM Business Partner, at the company's Web site. And check out DMC's offerings in the MC Showcase Buyer's Guide.

Kevin Forsythe has worked on IBM midrange systems for more than 20 years. With many years of experience in programming, analysis, consulting, and instruction, he is uniquely skilled at making difficult material more easily understood. As the lead instructor for DMC Consulting's AS/Credentials training classes, Kevin is responsible for developing up-to-date courseware as well as providing instruction on a wide range of topics. This comprehensive background includes practical application, education, and research and provides a perspective that allows him to help others steer their way through the technical maze that surrounds them.

Kevin speaks regularly at conferences and user group meetings, volunteers as a Subject Matter Expert for COMMON, has written numerous articles on a variety of iSeries topics, and authored the bestselling book SQL for eServer i5 and iSeries.

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: