db abstraction: sql design

Hi! I'm new to this mailing list. So if this post is off-topic, please tell me and I will try to post it in other lists. I'm currently developing an intranet solutions targeted to run with several different SQL database system such as MySQL, PostgreSQL, Oracle, Microsoft SQL Server and so on. For the database abstraction I use the abstraction layer provided by the PEAR class collection. And for the design of the tables I use a software called DeZign for database (very good, by the way; more information at http://www.datanamic.com/). With this software it's possible to develop tables and to export a SQL script for creating those tables on several different database server, especially those mentioned above. The problem I have is how to develop SQL querys (SELECT, INSERT, UPDATE) that are compatible with all the SQL database I wrote about before. Does anyone know whether a software like DeZign is also available for the development of SQL querys? Or is there any _good_ resource on the internet comparing the syntax of _all_ the SQL implementations of databases? I didn't find any such information at all. Thanks a lot in advance! Michael