What is the purpose of SQL’s HAVING operator? It seems to me to be unnecessary, since the WHERE operator can choose which records are to be included in the query. What am I missing?

–Rich

Don’t sweat it, Rich. This is a very common point of confusion. Let me try to straighten it out for you, and in the process I’ll add a tip that some of the more experienced readers may not have seen before.

Sometimes you can get the same result either WHERE or HAVING. The following two SQL commands produce the same result set. That is, both

Note: The code accompanying this article is available for download here.

Dear Intelligent Colleague:

I’ve been less than impressed with the results of keying invalid email addresses into database files, mainly because I’ve had to deal with some of that undeliverable email. I recently wrote a little RPG routine that checks for glaring errors in an email address. The people for whom I wrote it liked it and thought that you might find it helpful too.

My routine enforces the following few rules:

* No leading or embedded blanks.
* No question marks, exclamation points, or slashes.
*

What you can’t see can slow down i5 disk performance, particularly when you’re dealing with the lithium ion batteries that i5 I/O adapters use to provide hard disk drive caching. Fortunately, the system i5 will warn you about aging batteries but if you ignore its warnings, failed batteries can adversely affect disk drive performance. The good news is that it’s easy for IBM service to replace old batteries but there are a few tricks in determining when replacement is necessary.

Why Regular Battery Changes Are Important

Lithium ion battery packs provide power for disk caching on your i5 disk arrays.