Home > Articles > Data > DB2

SQL Standards and Guidelines for DB2 Developers

  • Print
  • + Share This
This chapter shows how to create a set of SQL standards and guidelines for developers to follow when running applications that involve DB2.
This chapter is from the book

Every IT shop that has applications involving DB2 should have a set of SQL standards and guidelines for its developers to follow. This chapter is a start for developers and project managers to use as part of their development. Once you have a set of standards and guidelines, be sure to enforce them. Every program should have code walkthroughs to ensure that standards and guidelines are being followed.

The standards and guidelines that follow serve multiple purposes:

  • Relate to performance
  • Alleviate abends and/or production incident reporting
  • Reduce I/O and CPU costs
  • Increase productivity
  • Improve client satisfaction
  • Improve readability and understandability

The standards and guidelines that follow are grouped into two separate areas: one specific to COBOL SQL developers and the other specific to all SQL developers (no matter the language in which they are embedding their SQL code).

For COBOL Developers

  1. The SQLCODE must be checked after every SQL statement. The Declare cursor statement is only a declarative, and it gets no return code from DB2. All other SQL calls get some return code. Return code data from the DB2 database system gets automatically loaded in the SQLCA communications area.
  2. Every program must include the SQLCA and a DCLGEN for each table being coded against. The DCLGEN is predefined with host variables that match the column definitions. They are used to select data into, insert and update from, and serve as the host variables in any Where clause.

    If DCLGEN fields are not being used, then any program declaring variables in the code must make sure that the variable being declared exactly matches the definition in DB2. If it doesn’t, then there is a possibility that DB2 may not choose an index to process. For example, if Column1 is defined as an Integer, then the host variable in COBOL should be defined as S9(9) comp.

  3. Every program must have a consistent DB2 abend routine. For batch programs, it is easiest to have a called program that handles the display of the SQLCA fields and calls the DSNTIAR DB2 routine to display further DB2 messages. For online programs, sometimes it is good to write out the SQLCA and DSNTIAR information to a file or table in order to fall back on errors that occur. The SQLCA contains a lot of information specific to a call that is critical to troubleshooting an error. It is important to write out all the information captured. Make sure that at least the SQLSTATE is displayed, along with the SQLCODE.
  4. Never code Select * in a program. Only code for the columns needed. If a program needs all the columns, then code each one. This will prevent an abend if a new column is ever added to the table. The fewer columns being brought into the program, the more efficient the processing. (See tuning tip #3 and tuning tip #29 in Chapter 1, “SQL Optimization Top 100+.”) More columns can have an effect on performance due to larger sort sizes, possible index-only processing, and join types. When DB2 looks at which join type is best, part of its analysis is the number of columns from each table being selected.
  5. Make sure any columns defined as Nullable contain a null indicator host variable as part of the Select, Insert, or Update statements. This is most important in Select statements because DB2 will return an invalid -305 SQLCODE when it returns a column of null to the program and there is no null indicator specified. These null indicators must be defined in working storage as Pic S9(4) Comp.

    It is preferable to code the VALUE, COALESCE, or IFNULL SQL scalar function for any nullable columns because the program will not receive null indicators from DB2. This will alleviate -305 SQL errors where a program is not set up to handle the null indicator. It will also spare the program from having to define the null indicators in working storage.

    For example, Select COALESCE(PK_ID, 0) will return the PK_ID value if there is one, or it will return a zero if it is null. This could also be coded with the VALUE and COALESCE functions. All three would return the same result. The default specified must match the column definition. For example, since PK_ID is numeric, then the default must be a numeric—in this case, zero.

  6. Any SQL statement that contains one of the following aggregate functions should have a Null-Indicator host variable as part of the select (MIN MAX, AVG, SUM). DB2 will return a null indicator to the program if it finds no data to process these functions, and the COBOL program will have to define a null indicator. If the program is not set up with a null indicator, an invalid -305 SQLCODE is returned. It is preferable to code the VALUE, COALESCE, or IFNULL function to alleviate any null indicator logic. For example:
    SELECT IFNULL(AVG(SALARY), 0)
    FROM EMP
    WHERE WORKDEPT = 'XYZ'

    This will either return the average if rows are found or a zero if no rows were met in order to calculate an average.

  7. Minimize the number of times cursors are opened and closed during execution. If most of the time the open cursor and fetch retrieves only one row, then code a simple Select statement and execute the cursor processing only when a -811 (duplicate rows) SQLCODE is returned.

    Do not break up processing into multiple cursors unless performance seems to be an issue. If it takes a seven-table join, then code all seven tables in one cursor and let DB2 do the work. When you break it up, the process usually takes longer due to the extra times DB2 is sent SQL statements to process. So break up the join only when all other tuning efforts have been applied. Typically it would be more efficient to execute a seven-table join.

  8. CASE expressions should always contain an ELSE clause. If none of the conditions in the CASE are met, then DB2 will return a null (via a null indicator) to the program. If the program is not set up to handle a null being returned from the CASE expression, then a -305 SQLCODE is returned, which usually causes the program to abend.
  9. Always display counts for the number of Selects, Inserts, Updates, Deletes, and Open cursors that have been executed in the program. The overhead in COBOL to define the counters and increment them through the processing is minimal to the overall runtime of the program. Displaying these counts provides invaluable information when problems occur, helping a developer figure out which program to look into. Make sure the counts are displayed on every abend and at the end of processing.
  10. Always display the values in host variables for a SQL statement that has an invalid SQL return code and the program goes into its abend error routine. Every developer knows how frustrating it is to have a program error out or even abend and not know what values were being processed.
  11. Watch out for any SQL warnings that may occur in an SQL statement. Most programs seem to ignore warnings that many times help to detect potential problems. There are two indications of a warning message in the SQLCA: One is a positive SQLCODE other than +100; the other is a W in the SQLCA’s SQLWARN0 field. When either of these exists, DB2 is issuing a warning that something worrisome happened on the prior call and that while you may have received data back, it may not be what you expected. When SQLWARN0 is a W, DB2 also provides helpful information about the problem in one or more of the other SQLWARNn fields. Also check warnings on every SQL statement return. For example:
    Evaluate SQLCODE
      When 0
          If SQLWARN0 = 'W'
              Display '***  Warning error ***'
              Display 'Sqlstate = ' Sqlstate
          End-If
      When Other
          ...
    End-Evaluate
  12. Take advantage of the SQLERRD (3) out of the SQLCA. The third occurrence of the SQLERRD array is one of the most useful fields in the SQLCA. This field is populated after a successful insert, update, or delete with a count of the number of rows inserted, updated, or deleted. This is not populated when a mass delete with no Where logic is coded or populated due to deletes affected by delete cascade.
  13. Take advantage of fetching rowsets in your cursor processing. (See tuning tip #46 in Chapter 1.) This should be strictly enforced for large cursors because of the runtime savings.
  14. Apply all calculations within the COBOL code and then move the value to a host variable. Then reference the host variable in the SQL statement. Keep calculations out of SQL statements whenever possible.
  15. Hard code any and all values known within an SQL statement. For example, if a program always processes the terminated rows on a table, then use the SQL statement Where Status_Code = ‘T’. This is extremely helpful especially if frequency value statistics are present for the different values of Status_Code in the catalog tables. (See tuning tip #10 in Chapter 1.)
  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020