02
Sat, Nov
2 New Articles

SQL 101: Simplifying Application Development with SQL Triggers, Part 1

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

Time to get trigger-happy (not in the western-movie way) as I’ll introduce you to your new best friend: the SQL trigger. Keep reading to find out what I’m talking about!

If you’re not familiar with the trigger concept in IBM i’s context, it is a Big Brother–like “thing” that keeps an eye on a table and, when a certain operation occurs, performs a predefined action. In a silly analogy, if a table was one of Pavlov’s dogs, and the INSERT/UPDATE/DELETE operation was the light the scientist controlled, then the trigger would be the reflex action causing the dog to come running and start drooling.

In a time when business applications are increasingly intertwined, it’s hard to keep track of events to make sure a certain action is met with the appropriate reaction. Consider an order-entry application. In the old days, there was only one way to enter orders in the system: an IBM i program. Today, the front-end of the application can be a web, mobile, or client/server application, which makes reacting to a new order much more complex.

Naturally, you can write specific code on each platform to perform the same actions, but that’s not very productive. Creating a trigger over the order master table that reacts to an INSERT or UPDATE operation and performs the necessary actions is much simpler and effective. There’s only one piece of code to maintain, and there’s also the guarantee that the necessary actions will be performed even when there’s a new interface writing data to the table.

Triggers are application-independent. They are user-written programs that are activated by the database manager when a data change is performed in the database. Once a trigger is in place, programmers and end users cannot circumvent it. When a trigger is activated, the control shifts from the program to the database manager. The operating system executes your coded trigger program to perform the actions you designed. The application waits until the trigger ends, and then gains control again. This might cause an application’s performance to degrade, because if the first trigger triggers other triggers (read it again, slower this time), it can take a while until the application regains control. (Note that I’m purposely not using the word “program.” This application can be on a web platform, a mobile platform, or any other platform application.) Even so, triggers excel at the following tasks:

  • Enforcing business rules, no matter how complex—A good example is the aforementioned order-entry scenario. Suppose you want to ensure that whenever you enter an order in your database, the customer you are dealing with has no bad credit history. A trigger associated with the order master table can perform this check consistently and take the appropriate actions.
  • Providing data validation and an audit trail—You might need to ensure that, whenever a salesperson enters an order, a representative is actually assigned to that particular customer. You also want to keep track of the violation attempts. Again, a trigger can be activated on the order master table to perform the validation and keep a log of the violators in a separate table.
  • Preserving data consistency across different tables—In this case, triggers can complement the referential integrity and check constraints mentioned earlier in the this series, because they can provide a much wider and more powerful range of data validation and business actions to be performed when data changes in your database.

Triggers are important stepping stones on the path to modernization because they allow you to reuse code, implementing the old Java maxim write once, run everywhere. The fact that the trigger resides in the database and acts directly over the database tables, regardless of the application(s) that caused it to take action, frees you from writing two or more versions of the same code in different languages. Furthermore, if applications evolve or are replaced, your trigger will still work seamlessly, as long as the new/changed applications still perform the same operations over the database tables. In the end, you’ll have a single program to maintain (the trigger) that RPG, C, JAVA, C#, or other languages will “call” when they perform I/O operations over your tables. This allows you to move your entire front-end from green-screens to a web app, while keeping the backbone business logic on the IBM i, which is one of the many forms modernization can take.

Now that you’re probably convinced of the advantages of using triggers, I’ll show you how to create and maintain them…in the next TechTip. Just note that, because this series is dedicated to SQL, I’ll focus on the instructions SQL provides for creating, changing, and delete triggers—CREATE TRIGGER, ALTER TRIGGER, and DROP TRIGGER, respectively—but you can also create external triggers, written in a high-level language like RPG. It’s also possible to create and delete triggers with CL, using the ADDPFTRG and RMVPFTRG commands, respectively.

Rafael Victoria-Pereira

Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.

Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.


MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.

Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Evolve Your RPG Coding: Move from OPM to ILE...and Beyond
Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques.
List Price $79.95

Now On Sale

Flexible Input, Dazzling Output with IBM i Flexible Input, Dazzling Output with IBM i
Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains.
List Price $79.95

Now On Sale

SQL for IBM i: A Database Modernization Guide SQL for IBM i: A Database Modernization Guide
Learn how to use SQL’s capabilities to modernize and enhance your IBM i database.
List Price $79.95

Now On Sale

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: