Thu, Jul
2 New Articles

TechTip: Table Expressions in SQL

  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times
From time to time, someone will ask me how to select, using only one query, customers who have maximum transactions (rows) from table EMP.This is an example of what table EMP looks like:



















Expected result:







I suggested using the table expression (temporary table) method as one of possible solutions for V4R5 and later OS/400 versions:

With XT as                                             
       (Select Lname, count(*) Rowcount  From EMP       
        Group by Lname)                                 
 SELECT Lname,count(*) from EMP Group by Lname          
   Having count(*)=(select max(Rowcount) from XT)  

Recently, this response attracted some attention and caused new questions about how and where it could be used.

Table expressions consist of nested table expressions and common table expressions.
Common table expressions can be used to store SELECT statements in an intermediate result table. They can be specified prior to main select in SELECT, INSERT, or CREATE VIEW statements. Table expressions can be helpful when the same result table needs to be shared in a main select.

Table expressions are preceded with the keyword WITH. Keyword AS specifies select for temporary table.

Here's another example: Suppose you have to clear the files in the XFLES library, and those files have not been used for three or more years. The file names all start with AP, AR, or GL.

You can use table expressions to save complicated selection and date manipulation.
In following example, OD is the outfile for the DSPOBJD command, and DUMMY is a one-record dummy file to get system directive and ALBR file (LIB, FIL 10 byte character fields). RUNSQLSTM puts data from the OD file into n ALBR file. The program reads that file and clears the selected files.

         DCLF  ALBR                                            
         DLTF     QTEMP/OD                                     
         CLRPFM *LIBL/ALBR                                     
         DSPOBJD   OBJ(XFLES/*ALL) OBJTYPE(*FILE) +          
                   OUTPUT(*OUTFILE) OUTFILE(QTEMP/OD)          
          /* Extract file names     */                                  
 READ:  RCVF                               
        CLRPFM &LIB/&FIL                      
         GOTO READ                                                                   

A source file of SQL statement is in YourLIB/QCLSRC ABC member type SQL:

INSERT INTO ALBR                                                 
 WITH AT AS(                                                       
  SELECT ODLBNM, ODOBNM,                                           
  CHAR(CASE WHEN ODUCEN='0' THEN '19'                              
                          WHEN ODUCEN='1' THEN '20' END)||                                                             convert         
             SUBSTR(ODUDAT ,5,2) ||SUBSTR(CHAR(ODUDAT),1,4) LSTDAT                        to  ccyymmdd
  FROM OD                                                            
  WHERE ODOBAT='PF' AND ODUCEN<>' ' AND                           
               SUBSTR(ODOBNM,1,2) IN ('AP', 'AR', 'GL'))         
FROM AT               
  WHERE LSTDAT< (SELECT                                            
    SUBSTR((CHAR(CAST(SUBSTR(CHAR(CURRENT TIMESTAMP),1,4)                           current date                             
    AS INTEGER)-3)),1,4)||SUBSTR(CHAR((CURRENT TIMESTAMP)),6,2)||                          subtract                 
       SUBSTR(CHAR((CURRENT TIMESTAMP)),9,2) CDAT                                                     3 years

If you got lost in date arithmetic as I did, don't worry. This is certainly not the best solution--even thought it works. The SQL statement--as well as the CL program--could be simplified. This is only an example of how to use temporary tables in RUNSQLSTM.
The same statement could be used as a QM Query.

By the way, if you don't want use temporary tables or MAX(...), just run the following:

Select a.Lname, count(*) as Rowcount
From emp a
Group by a.Lname 
       Having count(*)>=ALL                                      
       (select count(*)  from emp b   Group by b.Lname) 

--Issak Brender
This email address is being protected from spambots. You need JavaScript enabled to view it.



Support MC Press Online


Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: