Enhance performance by improving SQL coding practices.
Handing out blank checks in the world is definitely not a best practice if you're looking to avoid financial headaches and hardships. After a recent set of SQL performance engagements with clients, it's clear to me that a number of IBM i developers don't understand how to best check for blanks when using SQL with DB2 for i databases. As a result of these suboptimal coding practices, many developers are destined for performance and code maintenance headaches in the future.
This suboptimal SQL coding practice arises when a character column needs to be checked to determine if it contains all blank characters (also known as an empty string). Programmers believe that they have to help DB2 do this comparison instead of simply comparing the column to an empty string value with the following predicate: character_column = ''. This simple predicate is an SQL coding best practice whether the column is declared with a fixed-length or variable-length data type.
I think IBM i developers believe they must help DB2 with this comparison because the blank value being compared is a different length than the character column. Developers from other platforms are probably just propagating helper code that was necessary to deal with quirks in other database engines. In reality, the DB2 for i engine automatically adjusts for the lengths of the strings being different. Nevertheless, I've seen several developers "enhance" their SQL statements with the following types of predicates to "help" the DB2 engine determine whether a column contains all blanks:
- TRIM(TRAILING FROM character_column) = ''
- LENGTH(RTRIM(character_column)) = 0
- character_column = ' '
All of these enhanced comparison predicates correctly detect whether a column contains all blanks, but these enhancements aren't necessary. Instead, these enhancements make your SQL statements longer and harder to read, which results in SQL code that's harder to support and maintain over time. More importantly, performance is actually slower with the first two enhancement techniques that utilize built-in SQL functions (TRIM, LENGTH, RTRIM).
These two enhanced comparison techniques are primarily slower because they rely on unnecessary calls to SQL built-in functions. In addition, the usage of a function on a column comparison typically prevents the DB2 query optimizer from using an index to more efficiently perform the comparison. Performance tests that I ran showed the predicate method that uses a combination of the LENGTH and RTRIM functions to be almost 15% slower than the best practice comparison predicate of character_column = ''. And this measurement doesn't even take into account the potential for a much more dramatic performance improvement when using an index as part of the comparison processing.
If you eliminate these predicate enhancements on one of your SQL requests, the performance difference is probably not going to be noticeable on a single execution of that SQL statement. Correcting an SQL statement that's run multiple times by multiple jobs, however, will noticeably impact the performance of your applications and system.
This coding technique and other SQL coding best practices for performance are covered in the DB2 for i SQL Performance Workshop.
In summary, the key to preventing headaches with SQL blank checks is to employ the KISS principle of "Keep it simple, stupid." Avoid the urge to enhance your blank comparisons and simply use, character_column='' instead.
More 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.
TRY 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.
Forms 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.
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:
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.
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:
LATEST COMMENTS
MC Press Online