Make helper functions to have more Db agnostic code.

Like in your example could be something like this.

``` Pascal
if not TableExists('USERS') then
begin
  CreateTable('USERS').AddField('USERID', dtInt64)....
end;
```

Or how would be best to implelement and so,

Now the migration is just piece of SQL that is totally dependent on the current  Database, which is very good start tough.