• The State of the UNION

  March 17, 2010 Skip Marchesani

  DB2 for i supports the concept of union, which creates or derives a single result set table by combining two other result set tables, each of which was derived from a SELECT statement or another UNION. (See the discussion on cascading unions at the end of this article). A union is very useful when an SQL query must operate on two or more tables where JOIN cannot be used to produce the desired result set table. UNION is actually a clause for what is referred to in SQL terminology as a FULLSELECT. The combination of the first SELECT statement, followed

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• A Good Use for Global Variables

  March 17, 2010 Ted Holt

  Using global data (fields, variables and constants) is generally considered to be poor programming practice. One reason is that a subroutine or subprocedure that uses global data is not easily placed into service elsewhere. Another reason is that undesirable side effects may occur when one routine changes a variable that another routine uses. However, in some situations global data makes sense. I would like to provide one example. Assume a service program with several subprocedures. The source code for the module from which the service program is built looks like this: H nomain D/copy prototypes,mysvcpgm P DoThing1 b export D

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• Does An IPL Really Help Improve System Performance?

  March 17, 2010 Hey, Joe

  My i/OS system performance hasn’t been very good lately and my storage usage is starting to shoot up. I’m thinking I should IPL my System i 550 box to reset the system. Will an IPL help me regain storage and improve performance? –Tom The short answer is. . . it depends. Being IT professionals who also deal with Windows machines, sometimes our first response to bad system performance is to reboot the system. Fortunately for iSeries, System i, and Power i administrators, we don’t IPL our systems as much as others may reboot their Windows boxes, and we can usually

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• A Case for CASE

  March 10, 2010 Skip Marchesani

  The CASE operation is common to several programming languages on the IBM i. This includes SQL in DB2 for i, where it is available as the CASE statement for use in conjunction with a SELECT statement, or CASE expression for use in conjunction with the DB2 for i SQL Procedure Language. If you aren’t familiar with CASE from an SQL perspective, it’s a really effective mechanism to easily handle one or more forms of simple or complex conditional processing within the same SQL statement. The Two Forms of CASE There are two forms of CASE: Simple WHEN clause and searched

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• Job Descriptions: Underused and Underappreciated

  March 10, 2010 Ted Holt

  If every machine attached to the Internet were running a robust operating system like the IBM i, I doubt the malware problem would be nearly as severe as it is. Having said that, I wonder once again, as I do from time to time, why those who use IBM i neglect so many of its wonderful features. Today my thoughts turn to job descriptions. Before talking about job descriptions, let’s consider for a moment what a job is. Early in my career I acquired the bad habit of referring to a program or group of related programs as a job.

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• Admin Alert: A Skeleton Checklist for Performing Power i Upgrades

  March 10, 2010 Joe Hertvik

  A checklist is a great foundation for performing a complex job. Properly constructed, checklists allow you to quickly perform all necessary tasks to accomplish a goal. This week, I’ll present a skeleton checklist for performing Power i upgrades, listing off universal tasks that must be completed for a successful hardware or software upgrade. Use this checklist as a starting point for your own upgrades, adding specific tasks as needed. The Skeleton Checklist The skeleton checklist was created to ensure that whenever my shop undertook a hardware upgrade–whether it was a small upgrade or a complete system replacement–that we didn’t forget

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• Variable Program Calls in Free-Format RPG

  March 3, 2010 Jon Paris

  Many RPG programmers are familiar with the notion of using a variable, rather than a literal, to define the target of a program or procedure call. The problems usually begin when they try to utilize this technique in a /Free program because the “translation” of such calls into /Free is not an obvious one. The PGMCALL shown below is a simple “old-style” RPG program that demonstrates the basic principle for those of you unfamiliar with the technique. As you can see, it simply requests the name of a program to call, calls the program, and issues an error message if

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• How to Replace Display Files While They Are In Use

  March 3, 2010 Hey, Ted

  If you recompile a program while someone’s running it, it’s no big deal. The system moves the old object into library QRPLOBJ and the user never knows the difference. However, creating a display file is a different situation. You can’t replace a display while someone has a lock on it. Here’s a way to replace a display file, even while people are using it. To illustrate, assume a high-level program, MYHLLPGM, that uses display file MYDSPF. Most likely MYHLLPGM would be written in RPG or maybe COBOL. A user takes a menu option that calls MYHLLPGM, and the system locks

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• Admin Alert: Preparing Your CBU For a Real Emergency

  March 3, 2010 Joe Hertvik

  Alongside human tragedies, computer tragedies can also occur when a critical i/OS production system stops working and a shop must unexpectedly rely on its Capacity BackUp (CBU) system as its production box. Because a hard CBU cutover can offer more challenges than a planned switch test, here are some additional configuration tasks that can help you account for the unexpected challenges that go along with an emergency CBU switch over. When Those Who Stand and Wait No Longer Wait Like a good insurance policy, you hopefully never have to use your CBU. Unfortunately, there are a number of situations where

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• Naming Idiosyncrasies with the DB2 Storage Engine for MySQL

  February 24, 2010 Susan Gantner

  In a recent tip, I wrote about why I think MySQL is a great benefit to our platform. With its DB2 for i storage engine, MySQL allows yet one more way to access DB2 data. In this article, I’ll go into a few naming gotchas that can arise when using MySQL. But first I’ll describe some scenarios in which developers in today’s RPG shops may find themselves taking advantage of MySQL. The first scenario is one I touched on in my last tip: the availability of a huge array of open source (i.e., free or nearly free) applications written

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