Hi Will,

There are two problems that are going on.

1. IFNULL() doesn't have to know a return type.

2. If the types of arguments are different, we have to guess the return type.

Currently, we are not even guessing at a type when it comes to IFNULL(), but it is something that it worth for us to explore enhancing in the future.

But in the meantime, since you're using Postgres, can you give coalesce() a try instead of IFNULL()? coalesce() does actually guess at the return type is the same as the first parameter. It's not perfect, but it is better than no guessing like IFNULL() does.

Regards,

Jon