I have a customer that we are building a web based app for. It has been built using mysql and php and my customer wants to sell it to folks who have either mssql or mysql.
Since the code is currently specific to mysql, is there any way to allow either without extensively rewriting the application?
That would depend on how modular your code is currently. If you're currently using a database abstraction layer then it is relatively simple. If not, it's more challenging.