Stringscaping continues! This article explores functions to extract parts of a string that are similar to MS Excel functions and ways to stitch the strings back together. This “stitching” will introduce another function: LENGTH.

The functions discussed in the previous article allow you to add, replace, and remove characters from a string. While this is interesting and somewhat useful, being able to “stitch” two strings together is usually more useful. This article covers a group of functions that helps with that task.

You are probably familiar with MS Excel’s LEFT and RIGHT functions. LEFT and RIGHT allow you to extract the leftmost or rightmost n characters of a string. Most people know these functions but are not aware that there’s another one, named MID, that would be the long-lost twin brother of RPG’s %SUBSTR BIF if this were a soap opera. Well, LEFT and RIGHT also exist in SQL, along with the equivalent to the %SUBSTR BIF. While the following paragraphs won’t bring a lot of new information, I recommend you read them carefully, because I’ll use these functions in the “Embedding SQL in Your RPG Code” subseries as well as later in this series and also because they have some interesting details you might not be aware of.

Let’s begin with LEFT; just like its MS Excel namesake, LEFT returns the leftmost n characters of a given string. The following statement…

SELECT            LEFT(‘THIS IS A TEST‘, 7)

FROM        SYSIBM.SYSDUMMY1

…returns ‘THIS IS’ because I specified a 7 in the function’s second parameter, thus indicating that I wanted the first (or leftmost) 7 characters of the input string. You can probably guess what happens when I use the RIGHT function with the same parameters:

SELECT            RIGHT(‘THIS IS A TEST‘, 7)

FROM        SYSIBM.SYSDUMMY1

The system will return ‘ A TEST’ because those are the last (or rightmost) 7 characters of the input string. Of course, you can always use SQL’s SUBSTR function for the same purpose; you just need to adjust the parameters accordingly. Just like MS Excel’s MID function, SUBSTR has three parameters: input string, start position, and length to extract. Now I’ll indicate that I want to start in position 1 and that my intention is to extract 7 characters:

SELECT            SUBSTR(‘THIS IS A TEST‘, 1, 7)

FROM        SYSIBM.SYSDUMMY1

I’ll be getting the same ‘THIS IS’ string that the sample statement with the LEFT function produced. Slightly trickier is emulating the RIGHT function with SUBSTR because you need to know the length of the string in order to determine where to start extracting. For that, SQL has a LENGTH function, similar to its RPG’s %LEN; simply indicate a literal string, a field, or an expression and the system returns the length, in characters, of it. So I can use SUBSTR and LENGTH together in a little function-nesting example to emulate the RIGHT function’s functionality:

SELECT            SUBSTR(‘THIS IS A TEST‘, LENGTH(‘THIS IS A TEST’) - 6, 7)

FROM        SYSIBM.SYSDUMMY1

Such an expression is always evaluated from the inside out, i.e., the innermost function is evaluated first, its result is passed to the function that uses that innermost function as parameter, and so on, until the whole expression can be evaluated. In this case, this means that the system will calculate the expression LENGTH(‘THIS IS A TEST’) – 6 before performing the SUBSTRING operation. As expected, the final output is the same ‘ A TEST’ string that the aforementioned RIGHT function produced.

LEFT, RIGHT, and SUBSTR allow you to extract parts of a string. That covers the first part of “stitching” strings together. The actual stitching process can be easily performed with SQL’s concatenation operator—aka double pipe (||)—or the CONCAT function. Here’s an example that covers both methods:

SELECT            ‘THIS IS A ‘ || ‘TEST‘

, CONCAT(‘THIS IS A ‘, ‘TEST‘)

FROM        SYSIBM.SYSDUMMY1

Both operations return the exact same thing: ‘THIS IS A TEST‘. While the first method is similar to RPG’s concatenation method (simply replace the double pipe with a plus sign and you have RPG’s concatenation operation), the second one likens MS Excel’s Concatenate function. I usually use the double pipe, because of its similarity to RPG, but feel free to use whichever you prefer; the result will be the same.

This concludes the SQL string-related functions (not-so-brief) overview. I didn’t cover all the available functions, just the ones I think are the most useful. I’ll move on to the date-related functions, with the same approach: covering the most interesting with reasonable depth and a few examples.

If the examples provided were not enough to clear your doubts, use the comments section; I’ll try to help with additional examples and/or explanations.

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.

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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 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 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 Learn how to use SQL’s capabilities to modernize and enhance your IBM i database. List Price $79.95 Now On Sale