5.3. Compatibility between Databases

The variants of SQL used by different database implementations are very different.
The SQL standards define a very low common denominator, and even most SQL functions have different names and semantics in different implementations.
If you wish to support more than one implementation, you'll probably need more than one codebase.
It is a good idea to think what features you would need (at present and in the future) and choose one database that supports all of them.