• The Four Hundred
  • Subscribe
  • Media Kit
  • Contributors
  • About Us
  • Contact
Menu
  • The Four Hundred
  • Subscribe
  • Media Kit
  • Contributors
  • About Us
  • Contact
  • Guru: How To Cancel A Bad SQL Update

    May 15, 2017 Ted Holt

    In Three Ways To Manage Unmatched Data I wrote about the use of the RAISE_ERROR function to force a SELECT statement to cancel when unmatched data is considered a fatal error. Another good use of RAISE_ERROR is to force an UPDATE statement to cancel when an invalid condition occurs.

    To illustrate, imagine that you and I work in a factory. All factories have inventory. The people we serve purchase some inventory items and manufacture others. Our job is to write a program that will allow certain people to zero out the inventory balance for certain types of purchased items.

    The users will enter a series of item numbers into a database table (physical file) named ItemBal3. Our program is to set the quantity on hand to zero, but only for type 3 and type 4 items. Our program contains this UPDATE statement:

    update items as i
       set i.QtyOnHand = 0
     where i.type in ('3','4')
       and i.itemnumber in (select item from ItemBal3);
    
    
    If the users enter the ID numbers of items that are of other types, the program ignores those items.

    Let’s take it a step further. Suppose that the presence of some other type of item in ItemBal3 is an error that cannot be overlooked. In such a case, we can make the UPDATE cancel itself, like this:

    update items as i                                            
       set i.QtyOnHand =                                                  
              case when i.type in ('3','4') then 0                      
                   else raise_error ('97905',                           
                             'Non-purchased items cannot be zeroed') end
     where i.itemnumber in (select item from ItemBal3)

    Notice that the item type is no longer tested in the WHERE clause, but in the SET. If the database manager attempts to modify a type-3 or type-4 item, the case expression returns zero, which is assigned to the QtyOnHand column.

    But if the database manager attempts to modify an item of another type, the system calls the RAISE_ERROR function, which cancels the UPDATE and returns SQL state 97905 to the caller. If the program is running under commitment control, the database manager rolls back any items that were changed before the invalid item was encountered. I can illustrate with an example.

    Here is the item master table:

    Item number Description Type Quantity on hand
    A-1 3-inch Doodle 1 20
    A-3 5cm Spinkler 2 20
    A-7 #7 Hoozit 3 20
    B-1 Widget, size 8 4 20
    B-2 #12 Skyhook 5 20
    F-3 4-inch Floozle 6 20

    Here is ITEMBAL3.

    Item
    A-7
    B-1
    F-3

    If the system updates the items in the order in which they are listed, the quantity on hand for A-7 and B-1 changes from 20 to zero. But when it tries to update F-3, RAISE_ERROR cancels the UPDATE statement. Under commitment control, the quantity on hand reverts to 20. Without commitment control, A-7 and B-1 have a zero balance after the canceled UPDATE.

    Under commitment control, database integrity is preserved. You can find the problem, fix it, and restart the program.

    Without commitment control, you don’t know what you have. Good luck.

    RELATED STORY

    Three Ways To Manage Unmatched Data

    Share this:

    • Reddit
    • Facebook
    • LinkedIn
    • Twitter
    • Email

    Tags: Tags: FHG, Four Hundred Guru, SQL

    Sponsored by
    VISUAL LANSA 16 WEBINAR

    Trying to balance stability and agility in your IBM i environment?

    Join this webinar and explore Visual LANSA 16 – our enhanced professional low-code platform designed to help organizations running on IBM i evolve seamlessly for what’s next.

    🎙️VISUAL LANSA 16 WEBINAR

    Break Monolithic IBM i Applications and Unlock New Value

    Explore modernization without rewriting. Decouple monolithic applications and extend their value through integration with modern services, web frameworks, and cloud technologies.

    🗓️ July 10, 2025

    ⏰ 9 AM – 10 AM CDT (4 PM to 5 PM CEST)

    See the webinar schedule in your time zone

    Register to join the webinar now

    What to Expect

    • Get to know Visual LANSA 16, its core features, latest enhancements, and use cases
    • Understand how you can transition to a MACH-aligned architecture to enable faster innovation
    • Discover native REST APIs, WebView2 support, cloud-ready Azure licensing, and more to help transform and scale your IBM i applications

    Read more about V16 here.

    Share this:

    • Reddit
    • Facebook
    • LinkedIn
    • Twitter
    • Email

    COMMON Looking Youthful In 2017 HelpSystems Tackles IBM i Password Woes

    Leave a Reply Cancel reply

TFH Volume: 27 Issue: 33

This Issue Sponsored By

  • Profound Logic Software
  • Remain Software
  • ASNA
  • Linoma Software
  • Manta Technologies

Table of Contents

  • Open Source On IBM i: Let It Grow
  • HelpSystems Tackles IBM i Password Woes
  • Guru: How To Cancel A Bad SQL Update
  • COMMON Looking Youthful In 2017
  • The Five Things Clouds Need To Deliver For IBM i

Content archive

  • The Four Hundred
  • Four Hundred Stuff
  • Four Hundred Guru

Recent Posts

  • Liam Allan Shares What’s Coming Next With Code For IBM i
  • From Stable To Scalable: Visual LANSA 16 Powers IBM i Growth – Launching July 8
  • VS Code Will Be The Heart Of The Modern IBM i Platform
  • The AS/400: A 37-Year-Old Dog That Loves To Learn New Tricks
  • IBM i PTF Guide, Volume 27, Number 25
  • Meet The Next Gen Of IBMers Helping To Build IBM i
  • Looks Like IBM Is Building A Linux-Like PASE For IBM i After All
  • Will Independent IBM i Clouds Survive PowerVS?
  • Now, IBM Is Jacking Up Hardware Maintenance Prices
  • IBM i PTF Guide, Volume 27, Number 24

Subscribe

To get news from IT Jungle sent to your inbox every week, subscribe to our newsletter.

Pages

  • About Us
  • Contact
  • Contributors
  • Four Hundred Monitor
  • IBM i PTF Guide
  • Media Kit
  • Subscribe

Search

Copyright © 2025 IT Jungle