Wednesday, September 20, 2017

REGEXP for searching in strings

regexe instr to find instances of character in search string

Continuing my posts about the regular expressions introduced as part of IBM i Technical Refreshes to 7.2, TR6, and 7.3, TR2, I have struggled to come up with a good brief description that would suffice for this post's title. IBM's documentation describes this function as:

returns the starting position or the position after the end of the matched substring

After playing with this function for awhile I would describe it as: "returns the position where the searched pattern occurs, whether first or nth occurrence, in the source string". And I would have to admit that description is better than IBM's, but it not a good description either. It is probably best I start explaining how to use this function and you will be able to decide how you would describe it.

The format for this function is as follows:

Monday, September 18, 2017

Db2 for i poster

Scott Forstie, Db2 of i Team Leader, posted on twitter:

Are you bummed out that you don't have #Db2fori posters? Cheer up, you can have the pdf

The link to download the poster is here.

I have already printed mine and stuck it on the wall of my office.

Thursday, September 14, 2017

Writing to a User Space, update

get data from user space using pointer

After publishing my previous post several people contacted me regarding the method I had used to write data to and retrieve data from a User Space. In my example code I have used the QUSCHGUS API to write, and the QUSRTVUS API to retrieve. The messages asked why I had taken that approach versus using a pointer?

Either approach is valid, as they both perform the same function. But in the age of modern RPG code using pointers can be considered the better way to go. As I was remiss in my previous post I intend to make amends with this one.

One thing to be aware of if you are using your own User Spaces, rather than ones created by a list API, is your own does not contain the header information for the User Space. I will need to determine the equivalent data myself.

Wednesday, September 13, 2017

Writing to a User Space

using api to write to user space

I have written in the past about using User Spaces with List APIs. These earlier examples showed how I can retrieve data from a User Space, but how would I write or update my own User Space?

A User Space is like a data area, only bigger. While the maximum size of a data area is 2,000 bytes, a User Space can be up to 16,776,704 bytes. And I must use APIs to put and retrieve data in and out of a User Space.

Why would I use a User Space? They can be anything I want them to be.

  • Passing large number of parameters between programs
  • Share data between more than more than one program, I could use it to share data between more than one procedure
  • Snapshot of a file record (or table row)
  • I know of one software vendor that stores SQL statements in User Spaces that are later executed

Wednesday, September 6, 2017

REGEXP for count

regexe expression count used for counting characters in a string

With the latest IBM i Technical Refreshes to 7.2, TR6, and 7.3, TR2, a number regular expressions functions were added to Db2 for i (SQL). In this post I am going to describe the REGEXP_COUNT function.

Regular readers of this blog will know that I have already written about the REGEXP_LIKE. Rather than repeat a lot of the things I wrote about in the post I am just going to refer you to it at various time in this one.

The format for this function is as follows:

  REGEXP_COUNT(source-string, search-pattern, start-position, 

Tuesday, September 5, 2017

Glimpses to the future releases of IBM i

timeline of current and future releases of ibmi

Whenever I have seen this image in IBM's presentations I have wanted to get a copy to post in this blog. Why? It shows IBM's plans for the life of the current releases and the timeline for future releases of the IBM i operating system.

I am not so naive to think these dates are fixed, we all realize that the release dates of future releases, and the end of support for current releases, can change. The exception is IBM i 7.1, its end of support is set for April 30, 2018.

I still expect Technology Refreshes to be released twice a year. I do expect a new TR to be announced at the COMMON Fall conference, next month.

Wednesday, August 30, 2017

Using derived columns to sort files

using sql views and derived columns to sort the data in the results

My employer uses "descriptive" part numbers for the parts they manufacturer. Without going into too much information, "descriptive" part numbers contain information about the item within the part number, it could contain characters that describe the material used to make it and/or characters to denote its end use. I am often asked to create a report for certain collections of parts. These "collections" are identified by a range of characters in certain positions of the part number, and the sort order desired may not be in a simple sort order, I will explain what I mean by that later.

The "descriptive" part numbers I will be using in these example consists of three parts:

Wednesday, August 23, 2017

REGEXP like added to SQL

regular expression regex like

I can remember many years ago having a conversation with a non-AS400 (yes, it was that long ago) person about the programming environment we worked with. He scoffed at the AS400 stating he could never work on it as it did not support Regular Expressions. I am not going to describe in too much detail what Regular Expressions, sometimes called regex or regexp, are as others have done a good job doing that. To give a very simple explanation: it is a sequence of characters that define a search pattern, which is then used to find or find and replace parts of strings. If you are interested in learning more check the Wikipedia page about regular expressions here.

Within the Db2 for i PTFs that accompanied IBM i TR2 and 7.2 TR6 a number of regular expressions functions were introduced to SQL. I am not going to describe them all in one post, as it would be too long, as I feel they merit their own posts. To start this post is about the REGEXP_LIKE. I am just going to give a simple overview of how to use this, if you want more details or want to learn how to make complex statements I suggest you visit the page on IBM's KnowledgeCenter, link at the bottom of this post, or use your favorite search engine to search for "REGEXP_LIKE". The posts about REGEXP_LIKE for Oracle's PL/SQL I found helpful.

Tuesday, August 22, 2017

Finding the minimum value across several columns

minimum value of more than one column

Sometimes I find something that I think is cool, it may be something small, like this, but I feel it is worth sharing.

I was asked about how to find the minimum value from multiple columns. SQL offers us the MIN function for returning the smallest value from a column. I can use that to get the smallest value from multiple columns, and the smallest value from all of those columns.

I have a file with three fields containing the following numbers:

Wednesday, August 16, 2017

Sometimes a List API is better than the SQL View

use list api and user space to get data about spool files

Sometimes it is just "better" to use a list API than it is to use the SQL View that "replaced" it. This week has given me an example of this. I was asked to create a program that would allow users to email themselves reports. I knew I would have to present the users with a list of spool files from which they could select the one they would want to email.

"No problem", I thought, "I will just use the Output Queue Entries SQL View."

I created a View over the OUTPUT_QUEUE_ENTIRES View, and then created a program using a multiple row fetch to get more than one row from the View. In the "test" IBM i partition the program ran a bit slow the first time I ran it, then ran faster each time after as the DB2 query engine created a temporary access path for me. Being a "test" partition there are not many output queues or spool files when compared to the "live" partition. I moved the objects I created to "live" and called the program there. It took more than 20 minutes to load the subfile with the list of user's spool files. With several hundred users and a very large number of spool files (many thousands, does anyone ever delete spool files?) in the "live" partition it was searching through all of them to find the few spool files belonging to me. The time taken made this method unacceptable. Back to the "drawing board".