Our DBA had a problem. He was trying to figure out the best way to populate a bridge table with the full set of keys from two source tables. The answer was to do a simple Cartesian product. It hadn’t occurred to him. The problem was that he had it classified as the wrong way to do things. Not surprising, I guess … this site describing such joins points out that Cartesian joins are “usually done by mistake.”
Be sure not to exclude things from your arsenal of solutions by classifying them as “the wrong way to do things.” Sometimes the wrong thing is precisely what you need.