Fri, Jun
3 New Articles

TechTip: Combining Multiple Row Values into a Single Row with SQL in DB2 for i

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


Leverage recursive SQL to pivot row values into a single column.


Often, when looking at a report, a user prefers to see similar values grouped together on a single line of output instead of having those values spread across multiple lines of report. An example of that type of report is displayed in the table below. For each automobile make, the report lists all of the models that are currently in inventory in a single row of the report.





Malibu, Tahoe


Focus, Taurus, Fusion




This can be a challenging report to write because the auto make values are going to be scattered across different rows of the table, which stores the automobile inventory data as shown in the following table. Essentially, the report writer is being asked to pivot the row values up into a single column value for the report output.

















The recursive support provided by DB2 for i allows this challenging requirement to be solved with a single SQL statement. Obviously, a solution could be delivered by utilizing your favorite IBM i programming language. However, a recursive SQL solution requires fewer lines of code.


The following SQL SELECT statement transforms the raw table data in the second table into the desired report format in the first table. Let's walk through the key components of the SELECT statement that enables values from multiple rows to be delivered as a single-column value.


WITH numbered_sets(make, model, curr, prev) AS (

   SELECT make, model,

       ROW_NUMBER() OVER (PARTITION BY make ORDER BY model) AS curr,

       ROW_NUMBER() OVER (PARTITION BY make ORDER BY model) -1 AS prev

   FROM inventory)

SELECT make,

       MAX (TRIM(L ',' FROM

             CAST(SYS_CONNECT_BY_PATH(model, ',') AS VARCHAR(256)) ))

FROM numbered_sets

START WITH curr = 1

CONNECT BY make = PRIOR make AND prev = PRIOR curr



The statement uses a common table expression named numbered_sets to logically number and link each row that contains a model (e.g., Taurus) belonging to the same make (e.g., Ford). That logical numbering is accomplished with the ROW_NUMBER specification, which can be used to number each row in a set. The PARTITION BY clauses cause the numbering to start over at 1 once all of the rows associated with a single make have been numbered. The rationale behind two row-number values being assigned to each row will become clear when the recursive processing is discussed. Figure 1 gives you an idea of the row values produced by the table expression for rows in the inventory table that stored data for the Ford make.



Figure 1: This representation shows the numbered_sets table expression.


Now that the rows belonging to each make of automobile have been logically divided into numbered sets by the common table expression, let's examine the usage of recursion to combine these rows into a single value.


The CONNECT BY clause was made available in the IBM i 7.1 release to enable SQL to recursively navigate data relationships in your tables. The purpose of generating two sets of row numbers was to provide a way to link together the rows that share the same make value. The START WITH clause is even enough to understand it's stating that the recursive process should start with the first row in each set of automobile makes. For the set of Ford rows, that would be the row containing the Fusion model inventory data. The CONNECT BY clause contains two column comparisons that direct the recursive searches. The first comparison is easier to understand because it's stating that recursive processing should continue as long as it can find a row that contains the same make value.


The second comparison (prev = PRIOR curr) is more difficult to understand. That comparison is telling DB2 to find a row that contains a prev value that matches the curr value in the prior row of the data hierarchy. This comparison is represented with the arrows embedded in Figure 1. DB2 starts with the Focus row (curr=1) and then finds a match with the Fusion row because its prev value of 1 matches the curr value in the Focus row. The Taurus row will get matched on the next level of recursion because its prev value of 2 matches the curr value of the Fusion row. The recursive processing of the Ford numbered set will stop with the Fusion row because it won't find any more rows with a matching make value.


The CONNECT BY clause allows DB2 to logically link all of the rows sharing the same make value, but it's the SYS_CONNECT_BY_PATH function that combines all of the model values from each row into a single value. This function essentially concatenates each value in the specified column (model in this example) with the column values processed during prior recursive iterations to represent the path taken through your data. The second argument is a separator value (comma in this example), which is concatenated to the specified column value. This delimiter is concatenated to the beginning of the column value. This is the reason that the TRIM function is nested around the SYS_CONNECT_BY_PATH function to remove the comma separator value from the beginning of the generated path value.


The MAX function and GROUP BY clause are needed to compress the path value generated during the recursive processing. The path value is output for each recursive iteration, so without grouping the Ford set, output would look like the following:


Ford     Focus

Ford     Focus, Fusion

Ford     Focus, Fusion, Taurus


Grouping all of the Ford rows together results in the last value above being chosen as the MAX value since blank characters have a lesser value than non-blank characters.


I think this SELECT statement is a great example of how easy it is to leverage multiple SQL features on a single request to perform powerful data transformations.


Hopefully, this article starts you thinking about how to apply technologies such as recursion and table expressions to meet other business requirements. If you think you need more help getting proficient with the advanced SQL technologies discussed in this article, then you should consider the DB2 for i Advanced SQL offering.

Kent Milligan
Kent Milligan is a Senior Db2 for i Consultant in the IBM Lab Services Power Systems Delivery Practice.  Kent has over 25 years of experience as a Db2 for IBM i consultant and developer working out of the IBM Rochester lab. Prior to re-joining the DB2 for i Lab Services practice in 2020, Kent spent 5 years working on healthcare solutions powered by IBM Watson technologies. Kent is a sought-after speaker and author on Db2 for i & SQL topics.


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: