Wednesday, July 8, 2020

Make second line appear and disappear on a subfile

subfile that expands to a 2nd line and contracts

I was asked how to do this by someone who said that no-one in his department knew how to: have a second record appear in a subfile when a function key is pressed, and disappear when the function key was pressed again.

Fortunately this is a simple thing to do with just three keywords in the display file's DDS:


And there is not much we have to do in the RPG program that uses the subfile.

I have deliberately stripped down the display file and RPG code to what I consider a minimum to, in my opinion, makes it easier to understand.

Let me jump right in and show you the display file I will be using in this example:

Tuesday, July 7, 2020

Selects with Intersect to find common records in two files

sql selects with intersect to find common data

Having written about Selects with Union I thought it was time to mention to Selects with Intersect.

Select statements with the INTERSECT combines the matching results from two tables into one set of results. To reiterate "matching" means that the same value must appear in the given column(s) in both files.

I have two example tables with the same column names, they contain the following data:

Table 1 Table 2

Wednesday, July 1, 2020

Writing to the same spool file from multiple programs

output from 2 programs to same spool file

The question sounded simple: How can I write to the same spool file from two programs?

I have written before about copying from more than one spool file to create a new one. But this time I will be writing to the same spool file directly from two programs.

Let me start with the DDS for the printer file:

01 A          R HEADER
02 A                                     1'PAGE HEADER'
03 A                                      SKIPB(001)
04 A          R FORMAT01
05 A                                     1'PROGRAM 1'
06 A                                      SPACEB(001)
07 A            COUNTER        3  0     +2EDTCDE(Z)
08 A          R FORMAT02
09 A                                     1'PROGRAM 2'
10 A                                      SPACEB(001)
11 A            COUNTER   R             +2REFFLD(COUNTER *SRC)
12 A                                      EDTCDE(Z)
13 A          R ENDREPORT                                            
14 A                                     1'* * * END OF REPORT * * *'
15 A                                      SPACEB(001)

Tuesday, June 30, 2020

Subsystem status using SQL

check status of subsystem using new sql view

Last year I wrote about a way to check if a subsystem was active or not. The statement combined two table functions and could only check if a subsystem was active, if it was not returned in the results it was assumed to be inactive. Included in the latest round of Technology Refreshes, IBM i 7.4 TR2 and 7.3 TR8, is a new SQL View all about subsystems, now I can get the same information just from one View, including the status of the subsystem.

The information I am interested from the View SUBSYSTEM_INFO is:

  • Subsystem name and the library it resides in
  • Status: active, inactive, etc
  • Number of jobs currently running in the subsystem
  • Maximum number of jobs that could run in the subsystem
  • Job that is monitoring the subsystem

Thursday, June 25, 2020

Searching for reserved characters in SQL

search strings for sql special characters

SQL like all other programming languages has a number of characters that are reserved for certain uses. What happens if you need to search for one of those characters in a table or file? In this post I am going to give you two ways you can do this.

To show how this works I have a test file with five records in it:

100% REAL

What I want to do is…

  1. Find the record with the apostrophe ( ' ) in it
  2. Find the record with the percent sign ( % ) in it

Wednesday, June 24, 2020

Using SQL to validate packed fields

validate packed number fields with sql

When I heard of these three table functions being introduced as part of the latest round of Technology Refreshes, IBM i 7.4 TR2 and 7.3 TR8, I was really interested to know what they did as their names, "Validate data", really piqued my interested. These table functions will validate packed numeric fields at, what I like to call, three levels:

  1. VALIDATE_DATA:  validates at the member level
  2. VALIDATE_DATA_FILE:  validates at the file level
  3. VALIDATE_DATA_LIBRARY:  validates at the library level

These three exist in the SYSTOOLS library.

It is nigh impossible to put bad data into date, time, and timestamp fields in files. But it is not too hard to put bad data into a packed numeric field. While rare, I am seeing this more as data is taken from other types of databases and applications, and loaded into files in IBM i.

Wednesday, June 17, 2020

Control progression of cursor in display file

control cursor movement on dspf

The question was how to control the way the cursor moves from field to field on a display. The display had two columns of fields and the questioner wanted the cursor to progress down the first column's fields before moving to the top of the second column.

My example display file contains two records format. The first I will be using to demonstrate the default cursor progression, and the second how I can move down the first column's fields before moving over to the second column.

The DDS code for the first record format looks like:

A          R SCREEN0
A            Z001           3   B  2  3
A            Z002           3   B  2 10
A            Z003           3   B  3  3
A            Z004           3   B  3 10
A            Z005           3   B  4  3
A            Z006           3   B  4 10

Tuesday, June 16, 2020

Deleting spool files using SQL

deleting old spool files using sql procedure

Many of the IBM i partitions I have worked upon have had an issue of old spool files occupying valuable storage space. Since IBM i 7.2 there has been a way for me to analyze the spool files, using SQL, and make decisions on which would be deleted. The process of doing the deleting had to be entrusted to a program containing CL commands.

The latest round of Technology Refreshes, 7.4 TR2 and 7.3 TR8, gave me a way I can delete old spool files using a SQL procedure, DELETE_OLD_SPOOLED_FILES

Warning:  Use this SQL procedure carefully. If you do not you run the risk of deleting all spool files from your partition.

DELETE_OLD_SPOOLED_FILES has five parameters:

Wednesday, June 10, 2020

Happy 7th birthday RPGPGM.COM

Another year has passed and this blog has reached its seventh anniversary. We are living in interesting times with IBM i, and over the years I have been fortunate to write about many things, that in my opinion, have made significant improvements to programming with this operating system. As well as a whole lot of cool additions to Db2 for i (SQL). I have learn a lot from what I have written about, and I am sure that I write better code than I use to.

The past year has been an exciting time, not only for this blog but for me too. I would include the following as my personal high points, in no particular order:

Tuesday, June 9, 2020

Making a hash of records for comparisons

sql hash_row to allow comparison of records in files

Another addition to Db2 for i as part of the latest Technology Refreshes for IBM i 7.4 TR2 only, is the ability to create a hash value for a record from a file using the HASH_ROW SQL built in function. I am not going to describe what hash values are, if you are interested there is a Wikipedia article describing it. I am just going to say that hash-ing a string produces hexadecimal value of the data.

Previously I had been able to hash individual fields, or columns, using the various standards of hash. As HASH_ROW uses SHA512 I can do the same for a field using HASH_SHA512:

01  SELECT HASH_SHA512('A') AS "Hash",
02         LENGTH(TRIM(HASH_SHA512('A'))) AS "Length"