Designing A Generic Database API

Hi,

My current project requires me to convert a mysql based software to a more generic one. I started by designing separate db class files and separated the lower level connection queries from the business logic. By doing this, I now have mssql.class, mysql.class, sqllite.class etc..

But am not sure how to handle sql functions in queries. For instance, one of my queries need the use of a date function to add minutes to a db field.

In mysql, I accomplish this using

dbfield+interval '$arg' minute between date1 and date1


But in mssql I cannot use this type of query. It seems I'll have to use date_add() function. How do I handle this situation?

My frontend scripting language is php

Thanks d'advance
Celia