That's definitely something we spend a lot of time thinking about. We have to be able to support easy, exploratory programming but also be able to nail stuff do

That's definitely something we spend a lot of time thinking about. We have to be able to support easy, exploratory programming but also be able to nail stuff down if it ends up being used a lot. We have a bunch of ideas queued up. One of the simplest is generating fake data as you write code so that you have a better chance of noticing edge cases. We are also planning to proactively hint about integrity constraints (types, unique/foreign keys etc) eg if a column only contains integers, show a button that fixes the type to integer. There is an optional typing system in the wings too. There is also lots of similar research aimed at spreadsheets (eg http://eusesconsortium.org/wysiwyt.php http://eusesconsortium.org/wysiwyt.php) which we can borrow from.