Solar_Sql claims to have nearly-automatic database portability. All Solar_Sql methods should provide identical results regardless of the database backend. The only exception to this is that not all databases have the exact same SQL functions and column types available, particularly with respect to date and time values, as well as LIMIT offset support.
With that in mind, you should attempt to do the following to ensure the portability of database work across all supported backends:
Use Solar_Sql_Select whenever possible to construct SELECT statements. This will ensure your LIMIT clauses work properly on all databases; some, like Microsoft SQL Server, do not support LIMIT offsets, but Solar_Sql_Select has workarounds for those systems.
Use Solar_Sql_Model whenever possible to define and create your tables. Solar_Sql_Model creates column definitions in a database-portable fashion, so that you can write write queries in a standard way.
Try not to use use database-specific SQL functions like YEAR(), MONTH(), SUBSTR(), CONCAT(), and so on. If you need these functions, try to emulate them at your PHP layer instead of at the database layer.