SQL Select for different platforms

So fare we program an MIS System with VFP8 , designing the Database with Xcase and use Stonefield Toolkit. (250 Tabels)

For the next release we like to support different Backend Databases
For step one SQL Server, later Oracle ore what ever Database will be there.

We found out that the SQL syntax for VFP and SQL server has elements that are the same and some that are different.

We want to find a solution that can generate Platform specific SQL statements.

Their is a system variable that assigns a user to a Platform (VFP or SQLSERVER)

We are looking for a solution (code) that manages the differences .
Because we do not want to maintain different code for the platforms in the program code.

In the code the statement elements are for VFP. If the Variable says SQLSERVER the code should change the syntax. The result string will be handled with “cursoradapterclass” and will be send to the Backend database.

There must be a working solution around.
We where thinking of some PRG with case statements or a handling of a table that has the rules for the transformation in it.

Any suggestion with samples are welcome
Thanks in advance Dirk Bachmann