Already Running Another RDBMS?
If you're currently running another database system, should you convert to MySQL? Not necessarily. If you're happy with your current system, why switch? But if you feel constrained by what you're using, you definitely should consider MySQL. Perhaps performance of your current system is a concern, or it's proprietary and you don't like being locked into it. Perhaps you'd like to run on hardware that's not supported by your current system, or your software is provided in binary-only format and you'd really prefer to have the source available. Or maybe it just costs too much! All of these are reasons to look into MySQL. Use this book to familiarize yourself with MySQL's capabilities, contact the sales crew at MySQL AB, ask questions on the MySQL mailing lists, and you'll find the answers you need to make a decision.
One thing to keep in mind is that although all major database engines support SQL, each supports a somewhat different dialect. Check out the comparison page on the MySQL AB Web site at http://dev.mysql.com/tech-resources/crash-me.php to see which engines support which features. Then check the chapters in this book that deal with MySQL's SQL dialect and data types. You may decide that the version of SQL supported by your current RDBMS is too different and that porting your applications would involve significant effort.
Part of your evaluation should be to try porting a few examples, of course. This will give you valuable experience in making an assessment. One of MySQL AB's commitments is to an ongoing increased conformance to standard SQL. That has the practical consequence of eliminating porting roadblocks as time goes on, so the porting effort may turn out to be easier than you expect.