Where is this SQL that needs translating coming from? Did you write it (or another programmer on your team). Is it from a legacy codebase? Is it being machine generated by another program that you can't modify?
If you, or a team mate are writing the SQL, them SQL::Abstract might be an option. You write your query in a perl like syntax, and it turns it into SQL in whatever dialect you specify. It can't do everything, but does most thing fairly well, including joins of arbitrary complexity, however it is only practical if you are writing the queries, rather than something else.
If the SQL is hard coded into a legacy codebase, or is being generated by a legacy program, then I think you will have to write a translator yourself. The good news is doing so is a finite problem. If it is old hard coded SQL, then you just need to find them all and write translation. If it is an old generator, then it is unlikely to be generating anything unexpected (like a human programmer might), so again you need to figure out how it is building it's queries, and deconstruct them, so that you can re-generate them in the other dialect.