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Which is better? BETWEEN versus =

As all good DB2 developers know, there is frequently more than one way to write a SQL statement to return

the same results. But the performance that is another issue. In this quarters tip, we take a look at

BETWEEN and the equivalent combination of =.

The BETWEEN predicate is easier to understand and code than the equivalent combination of less than or

equal to (=). In past releases, in many cases it was more efficient, too.But today, in most cases, the DB2 Optimizer recognizes the two formulations as equivalent and there usually

is no performance benefit one way or the other.

Performance reasons aside, one BETWEEN predicate is simpler to code and maintain than multiple = predicates. For this reason, I tend to favor using BETWEEN. but not always. Consider the scenario of

comparing a host variable to two columns. Usually BETWEEN is used to compare one column to two

values, here shown using host variables:

WHERE COLUMN1 BETWEEN :HOST-VAR1 AND :HOST-VAR2

However, it is possible to use BETWEEN to compare one value to two columns, for example:

WHERE :HOST-VAR BETWEEN COLUMN1 AND COLUMN2

This statement should be changed to:

WHERE :HOST_VAR >= COLUMN1 AND :HOST-VAR = AND = 'H';

Or we could code MIDINIT BETWEEN 'H' AND 'Z' in place of MIDINIT >= 'H'. Of course, for either of

these solutions to work correctly we would need to know that MIDINIT never contained values that collatelower than the value 'A'.

So, as usual, there is no one size fits all answer to the question!


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Contribution by Craig Mullins

Craig S. Mullins, president and principal consultant of Mullins Consulting, Inc., is a data management

strategist, researcher, and consultant. He has nearly three decades of experience in all facets of database

systems development and has worked with mainframe DB2 since V1. You may know Craig from his popular

books: DB2 Developers Guide (with over 1500 pages of in-depth technical information on DB2 for z/OS)

and Database Administration: The Complete Guide to Practices and Procedures (the industrys only

comprehensive guide to heterogeneous database administration). Craig can be reached via his website atwww.craigsmullins.com.

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