Sun, May
7 New Articles

SQL 101: Time to Sum Up (and You’ll Want to Bookmark This Article)

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

We've now covered the most relevant aspects of SQL, providing practical and actionable information about SQL’s main topics. This article sums up the series to this point and contains links to the articles corresponding to the topics mentioned.

The database is so integrated into IBM i that you can program for years without having to explicitly use SQL. RPG provides native operation codes to manipulate data and uses “native” names for the data objects it handles. Therefore, an important first step is naming names—providing a list of SQL names and the corresponding RPG name:

  • Library = schema or collection
  • Physical file = table
  • Non-keyed logical file = view
  • Keyed logical file, access path, or index = index
  • Record = row
  • Field = column
  • Field reference file = catalog

The next step involved explaining the data manipulation instructions that SQL offers:

  • SELECT—For queries over native files (physical and logical) or SQL objects, such as tables and views, the SELECT instruction provides a simple yet powerful way to retrieve information from the database.
  • INSERTAdding records to a table is this SQL instruction’s purpose. You can insert a single record per statement by naming the columns and their respective values, or use a SELECT statement to read data from other sources and add the result of that query to a table.
  • UPDATE— “Massaging” data with DFU can be a nightmare; the UPDATE SQL instruction makes that task much easier and more flexible. I used an UPDATE statement to explain another predicate—EXISTS—to demonstrate how you can update a column, taking into consideration information coming from another table.
  • DELETE—SQL’s most dangerous statement after the DROP statement can act as sharply as a surgeon’s scalpel or as bluntly as Thor’s hammer; it all depends on the statement’s WHERE

I intentionally left out the MERGE instruction, because it can be confusing at first and it’s not crucial to proper DML. But don’t worry, I’ll get to it eventually!

The next few (okay, not so few) articles were about SQL column functions. These functions fall into two big categories:

  • Aggregate functions—These functions take a set of values (like a column of data) and return a single (aggregated) value result from the set of values. A few of the aggregate functions discussed include AVG, COUNT, and SUM.
  • Scalar functions—This group of functions acts over a value (a column or expression value) and allows you to simplify a series of tasks. I’ve discussed string functions such as ASCII, VARCHAR, LCASE, and TRIM, and date-related scalar functions, including TIMESTAMP, NOW, and DAYOFWEEK.

After a lengthy explanation about SQL statements and functions, I’ve talked about a few tools in which to practice your newly acquired SQL skills:

  • Interactive SQL, a green-screen command line tool, similar to QCMD
  • i Navigator’s Run SQL Scripts, a graphical, user-friendly, and functionality-laden tool
  • a nice open-source, database-agnostic tool

Then came the fun part: taking SQL into your familiar territory. The next few articles discussed and demonstrated how to embed SQL statements in fixed format RPG using C/EXEC SQL, C+, and C/END-SQL to identify the start, continuation, and end of an embedded SQL statement, respectively. In free format RPG, this is a simpler affair because you just need to write EXEC SQL and terminate the statement, which can span as many lines as you want, with a semicolon character.

Embedded SQL gets even more useful when you get it to “talk” with RPG. This is achieved by the host variables, which are regular RPG variables, preceded by a colon character (:) when used in an embedded SQL statement. An RPG source file with embedded SQL requires a pre-compilation step to convert the SQL to something the RPG compiler can swallow, so a different compilation command is required. The CRTSQLRPGI command can be used to create modules, programs, or service programs. I recommend that you always create modules and then bind them to programs or service programs as needed. Some practical examples on the usefulness of embedded SQL followed, namely the Rtv_DayOfWeek and Chg_Case functions.

Still on the embedded SQL topic, cursors were discussed as a way to navigate row by row in the results of an embedded SQL SELECT statement. Both static and dynamic cursors (“empty shells” filled at run time by the PREPARE statement) were discussed, as well as a couple of ways in which they can be useful. Finally, a way to embed a few more DML statements was discussed.

Even after all of this SQL stuff, you’re still an RPG programmer, and the bulk of your source code is still written in RPG. However, encapsulating RPG code in stored procedures and user-defined functions allows you to open your RPG code to the outside world without having to rewrite it. The articles on this topic offered only a shallow explanation that is good enough for you to start, but further reading and experimentation is advisable.

No SQL introduction would be complete without at least a about the Data Definition Language (DDL). This is IBM’s bet for the future of file definition. DDS stopped evolving a few releases ago, while DDL continued to received regular (and numerous) new features. This subset of articles presented schemas, tables, views and indexes, which can replace the familiar library, physical, and logical file constructs.

The most recent set of articles talked about triggers. These are time- and sometimes life-saving “things” that you can use to empower your database with event-based, automated, application-independent actions that can be written in SQL or a high-level language. However, these articles only covered SQL triggers and discussed a few of their possible uses: enforcing business rules, triggering cascade changes in the database, and keeping audit information. All of this is done without writing a single line of RPG code! It’s important to mention that triggers are a very powerful tool. The explanation provided here is good enough for you to start using them, but in no way should it be considered a comprehensive tutorial on triggers. There are great, free books on that, such as the Stored Procedures, Triggers and User-Defined Functions in DB2 Universal Database for iSeries Redbook.

But don’t worry, this is not the end! I thought this would be a good time to look back and take stock of the road travelled thus far. There’s a lot more to talk about, so our journey will continue!

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



Support MC Press Online

$0.00 Raised:

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: