23
Tue, Apr
1 New Articles
  1. You are here:  
  2. Home
  3. Programming
  4. SQL
  5. SQL 101: Date-Related Functions, Part 1—Converting Almost Anything to a Date, Time, or Timestamp

SQL 101: Date-Related Functions, Part 1—Converting Almost Anything to a Date, Time, or Timestamp

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

This subseries will cover the main date- and time-related functions SQL has to offer, providing examples of possible applications of this interesting and useful set of scalar functions.

I’ll start by showing how to convert other data types to Date, Time, and Timestamp data. Handling dates and times in RPG has always been a pain. It’s true that the new-ish BIFs help a lot, but apparently simple tasks such as determining the day of the week of a given date or finding out when will the next Monday occurs require loads of RPG code to implement. SQL offers a very interesting set of scalar functions that can really help when it comes to handling date-related data.

Let’s start with the basics. SQL has three date-related data types: Date, Time and Timestamp. You have probably used them in your RPG programs, or at least you have seen them defined in D-specs, with the D, T, and Z data type definition, respectively. But SQL’s data types are not an exact copy of their RPG counterparts. Here’s a quick definition of these three data types, taken from IBM’s DB2 for i Reference manual:

“Date

A date is a three-part value (year, month, and day) designating a point in time under the Gregorian calendar, which is assumed to have been in effect from the year 1 A.D. The range of the year part is 0001 to 9999. The date formats *JUL, *MDY, *DMY, and *YMD can only represent dates in the range 1940 through 2039. The range of the month part is 1 to 12. The range of the day part is 1 to x, where x is 28, 29, 30, or 31, depending on the month and year. The internal representation of a date is a string of 4 bytes that contains an integer. The integer (called the Scaliger number) represents the date.

Time

A time is a three-part value (hour, minute, and second) designating a time of day using a 24-hour clock. The range of the hour part is 0 to 24, while the range of the minute and second parts is 0 to 59. If the hour is 24, the minute and second specifications are both zero. The internal representation of a time is a string of 3 bytes. Each byte consists of two packed decimal digits. The first byte represents the hour, the second byte the minute, and the last byte the second.

Timestamp

A timestamp is a six or seven part value (year, month, day, hour, minute, second, and optional fractional second) that represents a date and time. The time portion of a timestamp value can include a specification of fractional seconds. The number of digits in the fractional seconds is specified using an attribute in the range from 0 to 12 with a default of 6. The internal representation of a timestamp is a string of between 7 and 13 bytes. The first 4 bytes represent the date, the next 3 bytes the time, and the last 0 to 6 bytes the fractional seconds.”

It’s a Date

So let’s start with the conversion functions that are directly related with the Date data type. The DATE function converts a date, a timestamp, a character string, a graphic string, or any numeric data type to a date data type. While the first two input data types are obvious—a Date data type doesn’t require conversion, and a timestamp is converted by simply dropping the time part of the timestamp—things get a little murky when the input parameter is a string. In this case, either a valid date representation in string format, such as ‘2014-11-16’ is provided or a 7-character string representing a date in yyyynnn format, where yyyy represents the year and nnn the number of days elapsed since January 1st, is provided; for instance, ‘2015035’ represents February 4th 2015. The numeric data type will be converted in similar fashion, but it will represent the number of days elapsed since January 1st 0001 (0001-01-01 in ISO date format). This means that DATE(35) returns a Date data type variable containing the 0001-02-04 date value. Here’s an example that illustrates the several options:

SELECT      DATE(‘2014-11-16’)

            , DATE(‘2015035’)

            , DATE(35)

FROM        SYSIBM.SYSDUMMY1

This statement returns three date data type values, holding the dates 2014-11-16, 2015-02-04 and 0001-02-04, respectively. I don’t know why, but I couldn’t get the third example to work in a V7R1 system. This feature doesn’t seem to be a novelty of V7R2, like the RPAD and LPAD functions I mentioned a few articles ago. IBM’s DB2 for i Reference manual doesn’t help either, because this is not marked as a new feature.

Making Time

The TIME function is somewhat similar to date: It returns a time data type value, converted from a date, a time, a timestamp, a character string, or a graphic string data type. Converting a date data type to a time data type results in 00:00:00 (or midnight); the time data type doesn’t actually require a conversion; in the timestamp data type case, the date part is dropped; finally, the strings must represent a valid date, time, or timestamp in order to be converted to a time data type value.

SELECT      TIME(‘2014-11-16-10.23.25’)

            , TIME(’13.15.45’)

 FROM       SYSIBM.SYSDUMMY1

This statement returns two time date type values, 10:23:25 and 13:15:45, respectively. Note that the first expression of the SELECT clause converts a string to timestamp and then that timestamp to time. Note that this last conversion would have failed if, for instance, the string contained ’25.15.45’, because this is not a valid time representation.

Seriously Accurate Date and Time: The Timestamp

The TIMESTAMP function is a bit more difficult to wrap your head around because of the way its parameters work. This function has two parameters. The first is conceptually similar to DATE and TIME’s first parameter: a date, a timestamp, or a string that represents a valid date or timestamp. The strangeness is in the second parameter: It can be either a date, a timestamp, or a string from which the system can extract a time or an integer constant representing the number of fractional seconds. In this case, the second parameter’s value must be in the range 0 through 12. Let me try to make this clearer with a couple of examples; first, a simple timestamp conversion using a Date data type value in the first parameter and a Time data type value in the second one:

SELECT      TIMESTAMP(DATE(‘2014-11-16’), TIME(’16.28.45’))

FROM        SYSIBM.SYSDUMMY1

The execution of this statement will produce a timestamp data type value of ‘2014-11-16-16.26.45.000000’. That’s fairly straightforward, right?

The next article will continue to discuss date-related scalar functions, covering a few that don’t have an RPG equivalent and that usually take a bit of coding to implement, such as the Day of the Week function, for instance. Until then, let me know what you think in the comments section below.

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

$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: