class A {
    String acc;
    static mapping = {
        table "A"
        tablePerHierarchy false
        acc column: 'a_acc',index: true,unique: true,length: 12
    }
}
class B extends A {
    String acc;
    static mapping = {
        table "B"
        id generator: 'assigned', name: 'acc' , column:'b_acc'
    }
}