UPDATED TO FIVE STARS: FIXED my own code; SEE COMMENTS in three star section -- Alex. Use mysqli, not mysql.
This widget is great for simple php code and I recommend it. But I get mixed and even inconsistent results making read or write calls to my hosted server mysql database. I'm using the twentyeleven theme.
The same script that executes great in a standalone test.php in my browser may run in a PHP Code Widget, or it may run OK but break the sidebar below the insertion point, or it may not run at all.
A single database call seems to work better than multiple calls in the same script or multiple scripts in successive PHP Code widgets.
In fairness, I've been coding in Perl and mysql for years (very helpful) but I've only been picking up PHP more recently. I can provide code samples, but not sure this is the right forum for that.
Any common experience, comment or suggestions? Thanks!