I just noticed Martijns reply, and just want to add a little.

1) Using double quotes makes your content case sensitive, something you
should only do if very intentional.

2) Using 0 indicates that you try to obtain a previous value, something
which normally is very dangerous in a multiuser environment. Generators are
outside of transaction control, and you have no guarantee that what is
returned is what you inserted 2 milliseconds ago (another user may have
incremented the generator in the meantime).

HTH,
Set