13
Wed, Nov
5 New Articles

Practical SQL: SQLCOD and SQLSTT

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

This article compares SQLCOD and SQLSTT and shows you how to avoid one of the primary gotchas you face when using SQLSTT.

 

Embedded SQL programming is one of the most productive additions ever made to the IBM i development environment. But it's rarely used to run the traditional example statements you see in the SQL programming books: statements that increase the price of every item by 15 percent. Instead, the most often used construct in the embedded SQL toolkit is the cursor, which essentially provides a dynamically built logical file to your RPG program. And like any logical file, an essential part of using the file is knowing when you've hit the end. RPG provides two variables: SQLCOD and SQLSTT. SQLSTT is the more standard technique, but its improved accuracy does not come without some cost. Fortunately, that cost is pretty low, and I'll even pick up the tab!

SQLCOD vs. SQLSTT

You can do your own research on which of these is better. SQLCOD and SQLSTT are the RPG variables that represent the standard SQL variables SQLCODE and SQLSTATE. A nice discussion of the topic can be found on the PostgreSQL site. If you do decide to move to SQLSTT, you will find that in nearly every case you can replace references to SQLCOD with very similar references to SQLSTT. Let's look at an example.

 

  exec sql declare c cursor for

    select CUCUST, CUNAME from CUSMAS

      order by CUNAME;

  exec sql open c;

  dow SQLCOD = 0;

    exec sql fetch next from c into :wCust, :wName;

    if SQLCOD = 0;

      exsr processCustomer;

    endif;

  enddo;

  exec sql close c;

 

Let me briefly review the code. First, I create a cursor over the customer master, retrieving the customer ID and name for every record order by customer name. I then open the cursor and start a loop in which I fetch data from the cursor into local variables wCust and wName. If the variable SQLCOD is zero, I process the values (in this case, by calling a subroutine). The code will loop as long as SQLCOD is zero, jumping up to fetch the next row. SQLCOD will return a value of 100 when there are no more rows to be fetched, and we drop out of the loop and close the cursor. Nothing to it. (Note that using a DOW checks for an error on the open cursor.)

 

The only change to this routine to get functionally (almost) equivalent code would be to change the SQLCOD = 0 to SQLSTT = *ZEROS. I use the figurative constant *ZEROS because SQLSTT is a character field, and I have to either use *ZEROS or else spell it out with '00000'. The better option of course is to define a named constant up in my D-specs, but I want you to see the actual values, and it's easier if I just hardcode them into the code. Don't you hardcode it, though; do as I say, not as I do!

 

This technique is pretty slick. It does ignore something, though, which is an SQL error. SQL errors tend to be silent; they return a value, but they don't send an exception message to the calling program, which in turn means they don't cause a hard halt to the user or the system operator. Whereas a record lock or a decimal data error makes itself known in native I/O, such things can kind of slide by under the radar unless you check for them.

 

So, you need to have a little additional code at the end of your loop. My code usually looks something like this:

 

  if SQLSTT <> '02000';

    exsr fatalError;

  endif;

 

An SQLSTT of '02000' means normal end of file. If I get out of my loop and I don't get that value, it's time to execute my fatal error logic. What sort of processing do I do? It depends on the situation. For an interactive program, it might be as simple as sending a message to the user and continuing on. In a batch job, I might dump the program and send a message to the system operator. This will happen whenever SQLSTT returns something that is not '00000' or '02000', and therein lies the problem.

SQL and Warning Messages

Let me illustrate the problem using a real-world example. Let's say I want to figure out the first order date for a customer. I want to process all customers, even those without orders. For customers that have no orders, I want the query to return a default date, say 12/31/2099. The SQL statement is easy:

 

  select CUCUST, ifnull(min(OHDATE),'2099-12-31')

    from CUSMAS left outer join ORDHDR on CUCUST = OHCUST

    order by CUCUST;

 

It uses a left outer join to return every row from the CUSMAS file, whether or not it finds a matching record in the ORDHDR file. If no matching records are found, the min(OHDATE) will return null. The code tests for this condition by using the ifnull function to replace null values with a default value of 2099-12-31. You can slip this into an RPG program and run it, and it will run fine. Fine, that is, right up until the point where it runs into a customer master without an associated order. And then suddenly your program will go BOOM!

 

Well, whether it goes boom or not depends on how you coded it. If you didn't include an end-of-loop test like the one above, the program will just think it hit end of file and will end normally—except that it didn't process all the records! Why is that? Well, a review of SQLSTT will be your first clue. As it turns out, SQLSTT returns the value '01003'. If you look up this error, you'll see something like this: "Null values were eliminated from the argument of a column function." Well, we know that! That's why we coded the ifnull function! But DB2 wants to be absolutely sure we know that something went awry, and so it gives us this little extra nudge by returning a warning value in SQLSTT.

 

How do you handle this situation?  First off, you have to know that you can get a warning error and that it's OK. You usually only know this after you get the error, so there is some level of empirical work involved, but as time goes on, you recognize potential problems. For example, this specific warning usually involves aggregate functions on left outer joins. Once you identify the potential problem, you can add a check to your program to not exit when a warning occurs. You might do something like this:

 

    if %subst(SQLSTT:1:2) <> '00'

      and %subst(SQLSTT:1:2) <> '01';

      iter;

    endif;

    exsr processCustomer;

 

Do you see how this works?  We check the first two characters to be either 00, which indicates a successful fetch, or 01, which identifies a warning condition. This might be too forgiving; there are a lot of warning conditions and many may not be as benign as the 01003 error. Click to see a list of the SQLSTT values. You may need to narrow down your check to specific values rather than just test the class (the first two digits).

 

To wrap this one up, let me give you very specific code for this situation, in which I check for either success or a null column:

 

  exec sql declare c cursor for

    select CUCUST, ifnull(min(OHDATE),'2099-12-31')

      from CUSMAS left outer join ORDHDR on CUCUST = OHCUST

      order by CUCUST;

  exec sql open c;

 

  dow SQLSTT = '00000'

    or SQLSTT = '01003';

 

    exec sql fetch next from c into :wCust, :wDate;

    if SQLSTT = '00000'

      or SQLSTT = '01003';

      exsr processCustomer;

    endif;

 

  enddo;

 

  if SQLSTT <> '02000';

    exsr fatalError;

  endif;

 

  exec sql close c;

 

That's it for this session. I hope it lets you unlock a little more of the power of SQL in your shop!

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

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 This email address is being protected from spambots. You need JavaScript enabled to view it..


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

$

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: