Make helper functions to have more Db agnostic code.

[TommiPrami]

Like in your example could be something like this.

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.

[AliDehbansiahkarbon]

Good idea.
Certainly, I will add more helper functions in this regard during the time.

[AliDehbansiahkarbon]

Like in your example could be something like this.

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.

Check the ORM samples.