I'm trying to figure out if there's a way to do a unique check across multiple tables. I'm checking the users ip for a survey, and we're creating a new one in which we don't want people who took the first one to take. I'm wondering if it's possible to do this in 1 statement? I know I can easily do this in 2 statements with a bit of server side logic, but I'm more curious about it in an educational way.
If MySQL were to support constraints would I be able to do a CHECK (count(table.ip) = 0), or would that not be possible since I'm referencing a different table? What would be the proper way to do that?
Thanks to anyone who knows!