Developing an application that can use several databases

[Fritjolf]

Hi.

I'm an experienced Delphi developer, working with v1 to 2010.
I have currently a lot of rather big database clients developed and
converted to Delphi 2010.
They use mainly Oracle. A few DB2 apps.

I see some applications made in delphi that can be installed on
several different databases....

I have often wondered how this is possible, and I would really like to
figure it out.
The database types might be different, the SQL is most definately
different.... ?

Does anyone have any idea of how to do this and I would really love a
link to a tutorial or a testproject on how to do this.

Best regards,

Fritjolf