29
Fri, Nov
0 New Articles

SQL 101 – DML recap – Between and In Predicates

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

It’s now time to do a Data Manipulation Language (DML) statements recap and use the sample UMADB database, presented in the previous two articles, in all the coming examples.

It will go over the SELECT, INSERT, UPDATE, and DELETE statements. However, this chapter won’t discuss the syntax of these statements. Here we will explain how you can write shorter and clearer statements by resorting to a few keywords that you might not be aware of. If you want to play around with the examples, be sure to restore the UMADB library. SQL 101 48 - UMADB.zip.

I’m going to assume that you’re familiar with the most commonly used DML statements and will not explain their syntax in depth, as they were previously covered in this series, starting here. Instead, I’ll focus on some details that can simplify the statements—for instance, shorter “implementations” of concepts. Having said that, let’s start with two of my personal favorites: BETWEEN and IN.

 

Using the BETWEEN and IN Predicates

Let’s get started with a simple yet very powerful keyword. If you started querying the IBM i’s database using Query/400 (as most of us did), one of the things you might miss is the RANGE keyword. This simple-to-use tool allows you specify the lower and upper limits of a range of values in a clear and concise way. What you might not know is that SQL has a RANGE equivalent: BETWEEN. This keyword’s equally simple to use, but it has a different syntax, which is closer to common English than the robot-speak of RANGE.

It’s easier to explain with an example, so let’s imagine that a user needs a list of all the university students that were born in the 1990s. The knee-jerk reaction would be to write something like this:

SELECT      STNM

            , STDB

   FROM     UMADB_CHP2.PFSTM

   WHERE    STDB >= 19900101

            AND STDB <= 20000101

;

Even though this statement is correct (assuming that the student’s birth date, column STDB of the PFSTM table, is in YYYYMMDD format), it can be made clearer with BETWEEN:

SELECT      STNM

            , STDB

   FROM     UMADB_CHP2.PFSTM

   WHERE    STDB BETWEEN 19900101 AND 20000101

;

Notice how using the BETWEEN predicate made the statement easier to read. By the way, I’m a big fan of clear code, so you’ll see a lot of indentation in my code examples. It makes the code easier to read and, more importantly, easier to maintain. For instance, if I want to add a new column to the query, I simply add a new line wherever I need to add it, and insert a comma followed by the column name. If all the columns are in the same line, this might not be so simple, especially in queries with a lot of columns. The only downside to this is that my queries tend to get a bit long. However, if you use IBM Navigator for i’s Run SQL Scripts or any other non-native query tool (IBM Rational Developer for i’s, WinSQL, Toad, DBeaver and so on – I covered a few of these previously, so if don’t know them, go and have a look, you might be positively surprised) this is not a big issue. All the examples shown here were written in Run SQL Scripts. You’ll notice the SQL syntax with the period (.) separating the library (schema) and file (table) names, instead of the system’s native syntax with the slash character (/) acting as a separator between the library (or schema) and the table, and the semicolon (;) terminating each statement.

Even if you knew BETWEEN, you might not know that you can invert the selection by adding a simple keyword: NOT. Here’s an example to illustrate what I mean: the user actually wanted a list of all the students who weren’t born in the 90s. Well, let’s not waste the statement we just wrote. Let’s modify it instead:

SELECT      STNM

            , STDB

   FROM     UMADB_CHP2.PFSTM

   WHERE    STDB NOT BETWEEN 19900101 AND 20000101

;

See how with a very simple change you can get the exact opposite result of the original query? You can use NOT in all sorts of ways to easily negate a comparison. It’s particularly useful when the opposite of a comparison is complex to write down. Instead, you can simply write NOT (original comparison), and you’re done. I’ll provide additional examples in a moment.

Another tedious and error-prone situation is when you want to find all the records that have one of several values in a given column. For instance, let’s say that someone wants a list of all the teachers with the rank of Dark Master, Maximus Praeceptor, or Praeceptor. (Yup, the teachers’ table is a bit quirky—actually, the entire database is! Take a moment to query the tables, and you’ll see what I mean.) In Query/400 you’d use LIST, but I noticed many people still write the comparison statement using something like this:

SELECT      TENM

, TETR

   FROM     UMADB_CHP2.PFTEM

   WHERE    TETR = 'Dark Master'

            OR TETR = 'Maximus Praeceptor'

            OR TETR = 'Praeceptor'

;

Instead of using LIST’s SQL equivalent IN keyword:

SELECT      TENM

, TETR

   FROM     UMADB_CHP2.PFTEM

   WHERE    TETR IN ('Dark Master', 'Maximus Praeceptor', 'Praeceptor')

;

Naturally, you can also use NOT to quickly list all the teachers who don’t hold one of these ranks:

SELECT      TENM, TETR

   FROM     UMADB_CHP2.PFTEM

   WHERE    TETR NOTIN ('Dark Master', 'Maximus Praeceptor', 'Praeceptor')

;

I’ve shown examples of BETWEEN using numeric value and IN using character values, mainly because this is their most common use. Keep in mind, though, that you can use these SQL predicates with any types of values and in any SQL clause that requires the use of a comparison, in addition to the WHERE clause. This is just the first taste of what’s coming! The next articles will cover other interesting DML operators, so stay tuned.

 

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

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: