I interpreted the question a bit differently than r937 did.
I'm assuming that fjg001 is asking if the SQL syntax that was written for PostgreSQL in the existing application will work against a MySQL database. It is possible that it might work, but it seems very unlikely that the SQL will work completely without changes.
Without knowing what the SQL code does, how it is organized, and how PostgreSQL specific it is, I can't even guess at how much work it will be to convert the application. The best that I can do is to suggest that you try it and see.
As r937 pointed out, the data conversion isn't hard at all. That should be little or no problem.
-PatP