I've been working on a project at work to process information imported into a SQL database through a front-end that isn't terribly configurable. So I have to glue all the data together in a long string, and then import it, then un-glue it and put each bit where it belongs.
I wrote a PHP script to do what I need. It works great, and has excellent error logging and runs fast. In fact, I was processing 2,000 records in about 8 seconds on the average. Today I processed somewhere around 70,000 records.
When I said it works great, I meant the program. The import, however, is subject to human error. As I was running this script, I'd run across records that were imported incorrectly, mislabeled, or otherwise generally borked. I had to fix those manually, there wasn't really any pattern to them.
I did, however, find another problem lurking in the database and wrote a small query to fix it. So while I trounced through the bowels of our SQL server and moved a bunch of stuff around, I did leave it in better condition than I found it…