OMG this is the tool that I've been waiting for! And thank God it's open source! I am so excited, this project has LOTS of potential, I am already imagining the future new features that until now it is absent in the current release.
One of them is the titled item: I think it should work in the way that graphically editing the query should be a (sort of) syntax-error-free action, or at least, if there is one (syntax error), the feedback (i.e. prompt syntax error) should be immediately shown right after the edit is done. In fact, I think everyone is expecting this kind of behaviour to be present in all visual development tools.
OK, I'm so used to MS' visual query designer that I'm comparing SQLeon to the MS one, but I'm sure that SQLeon will do better than all other (commercial) visual querying tools someday (although to my best of knowledge that's not much in the market/net), I'm waiting for this to happen with high hopes!
Keep up the good work~~~