There was a public service announcement I saw on TV in France which had a QR Code permanently displayed next to the chyron. It was amusing to me because the graphic was all white, so when the video behind it was light in color, the QR Code became unintelligible. I snapped a few quick shots as examples.
QR Code on TV on a black background
QR Code on TV on a white background
The double irony is that because they inverted the colors of the QR Code, many readers can’t decode it even when the background happens to be dark! (What’s white in the codes above should be black on a white background.) I struggled to get ZXing to decode it until I manually inverted the colors in Gimp. Same with the QR Droid app. And what does it encode, you might be curious to know? A generic Facebook page URL: http://www.facebook.com/consomag.TV?fref=ts
No, it’s not my QR code, but I thought it was an intriguing application of the technology.
Did we use it? No, we walked up to the counter like normal people. So what does the QR code encode? Good question: http://splitbread.com/1/16.html (location #1, table #16, I presume). For the record, I had a very tasty porchetta sandwich with cracklings and balsamic onion marmalade for dinner tonight. I’d definitely go back.
I want to query for parent records (those on the one side of a one-to-many relationship) that have no children that meet a specific set of criteria. The parents in the result set may have no children at all, or they may have many children, just none that meet the criteria. And I only want distinct parents in the result set. If a parent has two children that do not meet the criteria, I only want that parent returned once.
It turns out this type of behavior comes up more often than I’d expect. Imagine a database as part of a web service that has a table of users and a table logging the “lifecycle” email updates sent to those users. (Lifecycle emails are the periodic emails a service sends out over the course of your engagement with that service—they can be purely time based, e.g. 2 weeks after sign up, or they can be criteria based, e.g. after you place your first order. But in order to avoid being spammy/annoying, you usually only want to send these once, or once every X months.) In this scenario, I would want to query for all users (these are the parents) without a record of having received a certain type of email (the children). They may have received other emails, or they may have received no emails at all, but in either case, I want them returned in the result set. Let’s build up to the solution.
As I was getting perilously close to filling up my old 256GB hard drive, I decided to treat myself to a 512GB Samsung 840 Pro SSD, which created an opportunity to upgrade to the latest Ubuntu, a task I’d neglected for two years. I usually relish Ubuntu’s semiannual releases—that is, until the Unity user interface landed.