Sidebar

Practical SQL: Calling RPG from SQL, Part II

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

This second article on combining the strengths of RPG and SQL shows how to turn a stored procedure into a user-defined function (UDF).

 

In my previous article, I showed you how to create a stored procedure that will invoke an RPG program (or COBOL or CL or any other program, ILE or non-ILE). I also showed you how to test it and even explained the primary shortcoming of stored procedures: they can't be used in SELECT statements. I explained that in order to use external business logic inside of a SELECT statement, you need to use the other SQL extension technique, the user-defined function (UDF). This article shows how to create a UDF that uses your stored procedure.

A Quick Recap

In the previous article, I started with a program, STP001, that returns the price for an item. It's a very simple program that takes two parameters: the item number and the price. The first parameter is an input field that is used to calculate the price, which is then return in the second parameter. The program has no real business logic; it determines the price by checking the first character of the item number.

 

For the SQL part of my presentation, I then created a stored procedure using a CREATE PROCEDURE statement and showed how to test that stored procedure. Because stored procedures are primarily meant to be used within other programs (for example, via embedded SQL or ODBC), they aren't easy to test using some traditional ad hoc query tools. STRSQL doesn't like calling procedures with output parameters, so instead I suggested using iSeries Navigator, which is very friendly to all things SQL, including stored procedures.

Moving On to the UDF

In this article, I'm going to create a UDF to wrap the stored procedure in a way that will make it much more accessible to various tools, including the old tried and true STRSQL. Let me start, though, by introducing the concept of the UDF.

 

The primary mechanical difference between UDFs and stored procedures is how they interact with the caller. A call to a stored procedure is very much like a call to a program in RPG. The call consists of a fixed number of parameters of predetermined type and length. This includes the return value; if you want to return something, you provide a parameter. The called program will update the parameter with the resulting value.

 

One of the unique features of the program call architecture is that you can return multiple discrete result values, simply by adding more bidirectional parameters. This is very different from a UDF, which can return only a single value. All parameters to the UDF are defined to be input-only and cannot be changed. The only way to return data to the caller is through the (single) return value. It is this syntactical restriction, however, that allows the UDF to be used within SELECT statements. Let me demonstrate.

 

The first thing to do is to create the UDF. This UDF requires that the stored procedure GETPRICE be available. If you haven't already done so, please refer to the previous article and follow the steps there to create the GETPRICE stored procedure. Once you have the GETPRICE stored procedure in place, you can execute the following SQL.

 

create function MCP.GETPRICE

  (iItem char (15))

  returns decimal(9, 4)

  language sql deterministic

begin

  declare oPrice numeric (9,4);

  set price = 0;

  call MCP.GETPRICE (iItem, oPrice);

  return oPrice;

end;

 

This SQL statement creates a procedure named MCP.GETPRICE, which calls the stored procedure also named MCP.GETPRICE (one of my conventions is that if I'm wrapping a stored procedure in a UDF, I name them both the same). The primary purpose of the UDF is to act as an adapter between the bidirectional parameter list of the stored procedure and the input parameter/return value architecture used in SELECT statements. This parameter impedance mismatch is common in SQL, and the technique above can be used for other instances of the problem.

 

The concept is very straightforward:

 

  1. Create a temporary variable.
  2. Call the stored procedure passing the input values and the temporary variable.
  3. The stored procedure updates the temporary variable.
  4. After calling the stored procedure, return the contents of the temporary variable.

 

In the example above, the UDF creates a temporary variable oPrice, which is used as a bidirectional parameter to the stored procedure GETPRICE. Note that the UDF has only a single input parameter for the item number; it doesn't include the price in the parameter list. Instead, the price is going to be sent to the caller as the UDF's return value. This works for any number of input parameters; if the stored procedure had three input parameters and one output parameter, the UDF would have three parameters (all input by definition) and the return value would take the place of the output parameter. This works for any configuration, as long as the stored procedure has only one output parameter. If the stored procedure has multiple output parameters, you'll have to be more creative. For example, you might consider combining the return values into a delimited string. But let's continue with our scenario in which we have only a single return value.

 

The UDF is created, so now we can use it in pretty much any SQL statement. Let me illustrate with a simple example.

 

with Items (Item) as

  (select 'ABCD' from SYSIBM.SYSDUMMY1

   union select 'BCDA' from SYSIBM.SYSDUMMY1

   union select 'CDAB' from SYSIBM.SYSDUMMY1)

select Item, MCP.GETPRICE(cast(Item as char(15))) from Items;

 

The result looks like this:

 

Item   Price

ABCD   123.4560

BCDA   9.9990

CDAB   0.0235

 

This example looks a little complex, but really the first four lines of the statement are superfluous. They exist only to create the temporary table named Items with the three item numbers. In a production environment, you'd be using an existing Items table. I just wanted to show you an easy way to create a little temporary data. The actual meat of the statement is the SELECT statement in line 5, which invokes the GETPRICE UDF passing in the item number and returning the price. Effectively, you're calling RPG program STP001 for every line in the result set. Very nice indeed!

 

You may have noticed the CAST keyword; it converts the variable string 'ABCD' into a fixed-character field. This illustrates one important point: you have to be very careful that your parameter types match exactly what the UDF is expecting. If you don't, the system doesn't find the UDF and the statement fails, typically with an SQL0204 error.

Special Note for When Invoking Service Program Procedures

If you're an ILE programmer, you realize that procedures in ILE not only have a return value, but can also have bidirectional parameters. Neither stored procedures nor UDFs support both capabilities, so you lose certain functionality when wrapping procedures within SQL. Stored procedures support bidirectional parameters when invoking a service program procedure but will discard any returned value. On the other hand, UDFs honor the return value but have no way to handle any updates to the input parameters.

 

So, SQL can be used to provide access to service programs, but limitations exist and you may find yourself doing some creative programming to get around those limitations. Either that, or you can design your service programs in such a way that those procedures that will be called by SQL conform to the appropriate architecture (no return values for stored procedures and input-only parameters for UDFs).

 

This two-part article has given you the tools you need to integrate your natively programmed business logic into your SQL. We're not done yet, though; in a future article, I'll investigate the use of table procedures and functions that can return result sets rather than single values. Until then, good luck with your adventures in SQL integration!

as/400, os/400, iseries, system i, i5/os, ibm i, power systems, 6.1, 7.1, V7, V6R1

Joe Pluta

Joe Pluta is the founder and chief architect of Pluta Brothers Design, Inc. He has been extending the IBM midrange since the days of the IBM System/3. Joe uses WebSphere extensively, especially as the base for PSC/400, the only product that can move your legacy systems to the Web using simple green-screen commands. He has written several books, including Developing Web 2.0 Applications with EGL for IBM i, E-Deployment: The Fastest Path to the Web, Eclipse: Step by Step, and WDSC: Step by Step. Joe performs onsite mentoring and speaks at user groups around the country. You can reach him at joepluta@plutabrothers.com.


MC Press books written by Joe Pluta available now on the MC Press Bookstore.

Developing Web 2.0 Applications with EGL for IBM i Developing Web 2.0 Applications with EGL for IBM i
Joe Pluta introduces you to EGL Rich UI and IBM’s Rational Developer for the IBM i platform.
List Price $39.95

Now On Sale

WDSC: Step by Step WDSC: Step by Step
Discover incredibly powerful WDSC with this easy-to-understand yet thorough introduction.
List Price $74.95

Now On Sale

Eclipse: Step by Step Eclipse: Step by Step
Quickly get up to speed and productivity using Eclipse.
List Price $59.00

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

RESOURCE CENTER

  • WHITE PAPERS

  • WEBCAST

  • TRIAL SOFTWARE

  • White Paper: Node.js for Enterprise IBM i Modernization

    SB Profound WP 5539

    If your business is thinking about modernizing your legacy IBM i (also known as AS/400 or iSeries) applications, you will want to read this white paper first!

    Download this paper and learn how Node.js can ensure that you:
    - Modernize on-time and budget - no more lengthy, costly, disruptive app rewrites!
    - Retain your IBM i systems of record
    - Find and hire new development talent
    - Integrate new Node.js applications with your existing RPG, Java, .Net, and PHP apps
    - Extend your IBM i capabilties to include Watson API, Cloud, and Internet of Things


    Read Node.js for Enterprise IBM i Modernization Now!

     

  • Profound Logic Solution Guide

    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 companyare not aligned with the current IT environment.

    Get your copy of this important guide today!

     

  • 2022 IBM i Marketplace Survey Results

    Fortra2022 marks the eighth edition of the IBM i Marketplace Survey Results. Each year, Fortra captures data on how businesses use the IBM i platform and the IT and cybersecurity initiatives it supports.

    Over the years, this survey has become a true industry benchmark, revealing to readers the trends that are shaping and driving the market and providing insight into what the future may bring for this technology.

  • Brunswick bowls a perfect 300 with LANSA!

    FortraBrunswick is the leader in bowling products, services, and industry expertise for the development and renovation of new and existing bowling centers and mixed-use recreation facilities across the entertainment industry. However, the lifeblood of Brunswick’s capital equipment business was running on a 15-year-old software application written in Visual Basic 6 (VB6) with a SQL Server back-end. The application was at the end of its life and needed to be replaced.
    With the help of Visual LANSA, they found an easy-to-use, long-term platform that enabled their team to collaborate, innovate, and integrate with existing systems and databases within a single platform.
    Read the case study to learn how they achieved success and increased the speed of development by 30% with Visual LANSA.

     

  • Progressive Web Apps: Create a Universal Experience Across All Devices

    LANSAProgressive Web Apps allow you to reach anyone, anywhere, and on any device with a single unified codebase. This means that your applications—regardless of browser, device, or platform—instantly become more reliable and consistent. They are the present and future of application development, and more and more businesses are catching on.
    Download this whitepaper and learn:

    • How PWAs support fast application development and streamline DevOps
    • How to give your business a competitive edge using PWAs
    • What makes progressive web apps so versatile, both online and offline

     

     

  • The Power of Coding in a Low-Code Solution

    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:

    • Discover the benefits of Low-code's quick application creation
    • Understand the differences in model-based and language-based Low-Code platforms
    • Explore the strengths of LANSA's Low-Code Solution to Low-Code’s biggest drawbacks

     

     

  • Why Migrate When You Can Modernize?

    LANSABusiness 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.
    In this white paper, you’ll learn how to think of these issues as opportunities rather than problems. We’ll explore motivations to migrate or modernize, their risks and considerations you should be aware of before embarking on a (migration or modernization) project.
    Lastly, we’ll discuss how modernizing IBM i applications with optimized business workflows, integration with other technologies and new mobile and web user interfaces will enable IT – and the business – to experience time-added value and much more.

     

  • UPDATED: Developer Kit: Making a Business Case for Modernization and Beyond

    Profound Logic Software, Inc.Having trouble getting management approval for modernization projects? The problem may be you're not speaking enough "business" to them.

    This Developer Kit provides you study-backed data and a ready-to-use business case template to help get your very next development project approved!

  • What to Do When Your AS/400 Talent Retires

    FortraIT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators is small.

    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:

    • Why IBM i skills depletion is a top concern
    • How leading organizations are coping
    • Where automation will make the biggest impact

     

  • Node.js on IBM i Webinar Series Pt. 2: Setting Up Your Development Tools

    Profound Logic Software, Inc.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. In Part 2, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Attend this webinar to learn:

    • Different tools to develop Node.js applications on IBM i
    • Debugging Node.js
    • The basics of Git and tools to help those new to it
    • Using NodeRun.com as a pre-built development environment

     

     

  • Expert Tips for IBM i Security: Beyond the Basics

    SB PowerTech WC GenericIn this session, IBM i security expert Robin Tatam provides a quick recap of IBM i security basics and guides you through some advanced cybersecurity techniques that can help you take data protection to the next level. Robin will cover:

    • Reducing the risk posed by special authorities
    • Establishing object-level security
    • Overseeing user actions and data access

    Don't miss this chance to take your knowledge of IBM i security beyond the basics.

     

     

  • 5 IBM i Security Quick Wins

    SB PowerTech WC GenericIn today’s threat landscape, upper management is laser-focused on cybersecurity. You need to make progress in securing your systems—and make it fast.
    There’s no shortage of actions you could take, but what tactics will actually deliver the results you need? And how can you find a security strategy that fits your budget and time constraints?
    Join top IBM i security expert Robin Tatam as he outlines the five fastest and most impactful changes you can make to strengthen IBM i security this year.
    Your system didn’t become unsecure overnight and you won’t be able to turn it around overnight either. But quick wins are possible with IBM i security, and Robin Tatam will show you how to achieve them.

  • Security Bulletin: Malware Infection Discovered on IBM i Server!

    SB PowerTech WC GenericMalicious programs can bring entire businesses to their knees—and IBM i shops are not immune. It’s critical to grasp the true impact malware can have on IBM i and the network that connects to it. Attend this webinar to gain a thorough understanding of the relationships between:

    • Viruses, native objects, and the integrated file system (IFS)
    • Power Systems and Windows-based viruses and malware
    • PC-based anti-virus scanning versus native IBM i scanning

    There are a number of ways you can minimize your exposure to viruses. IBM i security expert Sandi Moore explains the facts, including how to ensure you're fully protected and compliant with regulations such as PCI.

     

     

  • Encryption on IBM i Simplified

    SB PowerTech WC GenericDB2 Field Procedures (FieldProcs) were introduced in IBM i 7.1 and have greatly simplified encryption, often without requiring any application changes. Now you can quickly encrypt sensitive data on the IBM i including PII, PCI, PHI data in your physical files and tables.
    Watch this webinar to learn how you can quickly implement encryption on the IBM i. During the webinar, security expert Robin Tatam will show you how to:

    • Use Field Procedures to automate encryption and decryption
    • Restrict and mask field level access by user or group
    • Meet compliance requirements with effective key management and audit trails

     

  • Lessons Learned from IBM i Cyber Attacks

    SB PowerTech WC GenericDespite the many options IBM has provided to protect your systems and data, many organizations still struggle to apply appropriate security controls.
    In this webinar, you'll get insight into how the criminals accessed these systems, the fallout from these attacks, and how the incidents could have been avoided by following security best practices.

    • Learn which security gaps cyber criminals love most
    • Find out how other IBM i organizations have fallen victim
    • Get the details on policies and processes you can implement to protect your organization, even when staff works from home

    You will learn the steps you can take to avoid the mistakes made in these examples, as well as other inadequate and misconfigured settings that put businesses at risk.

     

     

  • The Power of Coding in a Low-Code Solution

    SB PowerTech WC GenericWhen 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:

    • Discover the benefits of Low-code's quick application creation
    • Understand the differences in model-based and language-based Low-Code platforms
    • Explore the strengths of LANSA's Low-Code Solution to Low-Code’s biggest drawbacks

     

     

  • Node Webinar Series Pt. 1: The World of Node.js on IBM i

    SB Profound WC GenericHave 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.
    Part 1 will teach you what Node.js is, why it's a great option for IBM i shops, and how to take advantage of the ecosystem surrounding Node.
    In addition to background information, our Director of Product Development Scott Klement will demonstrate applications that take advantage of the Node Package Manager (npm).
    Watch Now.

  • The Biggest Mistakes in IBM i Security

    SB Profound WC Generic The Biggest Mistakes in IBM i Security
    Here’s the harsh reality: cybersecurity pros have to get their jobs right every single day, while an attacker only has to succeed once to do incredible damage.
    Whether that’s thousands of exposed records, millions of dollars in fines and legal fees, or diminished share value, it’s easy to judge organizations that fall victim. IBM i enjoys an enviable reputation for security, but no system is impervious to mistakes.
    Join this webinar to learn about the biggest errors made when securing a Power Systems server.
    This knowledge is critical for ensuring integrity of your application data and preventing you from becoming the next Equifax. It’s also essential for complying with all formal regulations, including SOX, PCI, GDPR, and HIPAA
    Watch Now.

  • Comply in 5! Well, actually UNDER 5 minutes!!

    SB CYBRA PPL 5382

    TRY 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.

    Request your trial now!

  • Backup and Recovery on IBM i: Your Strategy for the Unexpected

    FortraRobot automates the routine 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:
    - Simplified backup procedures
    - Easy data encryption
    - Save media management
    - Guided restoration
    - Seamless product integration
    Make sure your data survives when catastrophe hits. Try the Robot Backup and Recovery Solution FREE for 30 days.

  • Manage IBM i Messages by Exception with Robot

    SB HelpSystems SC 5413Managing messages on your IBM i can be more than a full-time job if you have to do it manually. 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:
    - Automated message management
    - Tailored notifications and automatic escalation
    - System-wide control of your IBM i partitions
    - Two-way system notifications from your mobile device
    - Seamless product integration
    Try the Robot Message Management Solution FREE for 30 days.

  • Easiest Way to Save Money? Stop Printing IBM i Reports

    FortraRobot 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:

    - Automated report distribution
    - View online without delay
    - Browser interface to make notes
    - Custom retention capabilities
    - Seamless product integration
    Rerun another report? Never again. Try the Robot Report Management Solution FREE for 30 days.

  • Hassle-Free IBM i Operations around the Clock

    SB HelpSystems SC 5413For over 30 years, Robot has been a leader in systems management for IBM i.
    Manage your job schedule with the Robot Job Scheduling Solution. Key features include:
    - Automated batch, interactive, and cross-platform scheduling
    - Event-driven dependency processing
    - Centralized monitoring and reporting
    - Audit log and ready-to-use reports
    - Seamless product integration
    Scale your software, not your staff. Try the Robot Job Scheduling Solution FREE for 30 days.