21
Fri, Jun
3 New Articles

Practical SQL: Prepared Statement Magic

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

SQL goes from flexible to downright magic when you take advantage of prepared statements.

If you’ve followed me over the years, you know that a lot of what I do centers around data analysis. Even as the industry trends toward transferring our data to a data warehouse (or data lake, nowadays), I still spend a lot of time taking existing data and massaging it into actionable business information for my customers. This involves both transactional data and configuration data (what we used to call master data). And even when we do use external data processing of one kind or another, oftentimes our data needs to be reviewed and cleansed before we can export it. For configuration data, one of the biggest issues is to find outliers, and that can be quite the feat.

Statement of Work

Today’s discussion is about finding unused fields and unusual values. We can take a simple case, the ubiquitous item definition file. Every ERP system has one; many have more than one. But let’s take a minimal case of a system with a single item file with a set of fields. Let’s do a short list: item number, item status, item description, item type, item group, item planner, unit of measure, and one of my favorites, harmonized system (HS) code. Most of those should be pretty self-explanatory, but we can identify a couple of immediate characteristics. Some are unique values (such as item number) while others are codes that belong to a limited list, such as unit of measure and HS code. Of the latter, some codes are externally defined (like HS code) while others are arbitrary values whose meaning is determined by the business.

When preparing for export, often one of the first things we need to do is review the data for consistency. These reviews typically lead to cleanup projects where someone in the business decides what to do with the various outliers. But before they can do that, someone has to build the list for them to review. It’s not hard for one file, but recently I had to do that for a number of files and fields, and that’s what led me to the techniques in this article.

Simple but Not Easy

I said it’s not hard for one file. Even that is a little misleading. Let’s decide what we’re going to do. I started by building a little field analysis file. This file has four fields: file name, field name, field value, and count. The idea was just to be able to store the analysis of the fields. And how would we populate the file? Well, assuming the fields in the analysis file are FAFILE, FAFIELD, FAVALUE, and FACOUNT, it wouldn’t be too hard to add, say, the statistics for the HS code in the item master. Assuming the field is IMHSCD in ITMMAS, the SQL is pretty simple:

INSERT INTO FLDANL

SELECT 'ITMMAS', 'IMHSCD', IMHSCD, COUNT(*)

   FROM ITMMAS GROUP BY IMHSCD ORDER BY 1

I threw in the ORDER BY clause just because that makes it easier to review the results quickly, even without a key on the file. But I immediately run into a few issues. First, I have to do this for every field in the file. That’s not too difficult when you have a few fields, but it quickly gets prohibitive when dealing with dozens of files with hundreds of fields each, which is typical in a modern ERP system. And if this task needs to be done more than once or twice, there needs to be a way to mechanize it. Second, I have to be careful not to inundate this file with those cases where every record has a different value, such as the item number. I have to figure out how to identify those fields with too many values for distinct analysis.

Serving with Distinction

I decided on a hybrid approach. First, every field would have a special record where the value “*DISTINCT” would indicate that the count was the number of distinct values in the file. Yes, I realize this breaks down for any field where the actual value is *DISTINCT, but that becomes less of an issue with the next change. What I did was then decide to only add additional records to the file if the number of distinct values was below an arbitrary threshold, in this case fewer than five distinct entries. So let’s assume that our item file has 1,000 records and that 500 of the items are accounted for in LBS, 300 in FT, and 200 in EA. I start by getting the count of distinct values:

INSERT INTO FLDANL

SELECT 'ITMMAS', 'IMUOM', '*DISTINCT', COUNT(DISTINCT IMUOM) FROM ITMMAS

I run this statement for each selected field. Then, for each field having a count less than five, I run the previous INSERT statement that adds the distinct values for that field. Executing this technique manually for the fields IMITEM and IMUOM (item number and unit of measure), I end up with these entries in the analysis file:

File

Field

Value

Count

ITMMAS

IMITEM

*DISTINCT

1000

IMTMAS

IMUOM

*DISTINCT

3

IMTMAS

IMUOM

EA

200

IMTMAS

IMUOM

FT

300

IMTMAS

IMUOM

LBS

500

Since there are so many distinct values for IMITEM, I don’t make entries for the individual cases.

Automating the Process

As noted, this is easy with a small number of fields. I can run the three SQL statements pretty easily. I can even put them in a script and run them repeatedly. But things start to get difficult as the number of fields increases. That’s what led me to an SQL approach, which in turn led me to write some code for this. To do this, I needed to use embedded SQL, but that was going to be tricky. The first issue is that embedded SQL won’t let us use variables to define table and column names (file and field name to us RPG folks). This will not work:

EXEC SQL 'SET :FACOUNT = (SELECT COUNT(DISTINCT :FAFIELD)'  

       + ' FROM :FAFILE';

So we have to go to the prepared statement approach. I was hoping this would do the trick:

P1 = 'SET ? = (SELECT COUNT(DISTINCT ' + %TRIM(FAFIELD)

   + ') FROM ' + %TRIM(FAFILE) + ')';                

EXEC SQL PREPARE S1 FROM :P1;                                

EXEC SQL EXECUTE S1 INTO :FACOUNT;                                        

But while DB2 supports EXECUTE…INTO, ILE RPG with embedded SQL does not. And that’s where I got stuck for a minute until I came up with the SQL magic for this article. I created a global variable called CDISTINCT and then just finished my code this way:

P1 = 'SET CDISTINCT = (SELECT COUNT(DISTINCT ' + %TRIM(FAFIELD)

   + ') FROM ' + %TRIM(FAFILE) + ')';                

EXEC SQL PREPARE S1 FROM :P1;                                

EXEC SQL EXECUTE S1;                                        

EXEC SQL SET :FACOUNT = CDISTINCT;                            

The prepared statement puts the number of distinct values into the global variable CDISTINCT, and then the last statement pulls that value into the field FACOUNT. At that point, I can write the record. I can then write the record or use an INSERT to add it. All that remains is the logic to insert the actual distinct values when the count is below the threshold.

IF FACOUNT < 5;                                          

P2 = 'INSERT INTO FLDANL SELECT '                      

     + '''' + %TRIM(FAFILE) + ''''                    

     + ', ''' + %TRIM(FAFIELD) + ''''                      

     + ', CHAR(' + %TRIM(FAFIELD) + ')'                    

     + ', COUNT(*) FROM ' + %TRIM(FAFILE)

     + ' GROUP BY CHAR(' + %TRIM(FAFIELD) + ') ORDER BY 3';

EXEC SQL PREPARE S2 FROM :P2;                          

EXEC SQL EXECUTE S2;                                  

ENDIF;                                                  

And there you have it! You drive this by reading through a list of fields (maybe from DSPFFD to an output file) and putting the file and field names into FAFILE and FAFIELD. These SQL statements then generate the distinct value analysis.

Not a Silver Bullet

While this technique is slick and takes advantage of some advanced SQL capabilities, the most important caveat is that this sort of analysis works best on smaller files, with tens of thousands of records, not hundreds of millions. That’s because most databases don’t have an index for every field, so the COUNT DISTINCT is going to have to do a check of every record. This will involve a lot of data access. But that aside, this is a great analysis tool, a good basis for other low-level file analysis, and a way to polish your prepared statement skills. Enjoy!

 

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

$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: