the problem is that in this case it would happily create the tables while on H2 and satisfy your need, but would completely bork the other databases.

but how is that handled in Keycloak? Is there something different special?

A) prepare migrations for H2

How does the migration support change that? I mean, when I start from scratch, using 1.0.3 as the first version. How helps the migration support for H2 that I am not running into this error. This error occurs when I extract wildfly.zip and deploy the 1.0.x build, no migration touched