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

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                 

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