Since Oracle's acquisition of Sun several years ago, it now offers certifications for both its flagship database, Oracle, and also for MySQL. If you are looking to get an 'Oracle' database certification, which of the two makes sense to pursue? There is value in gaining database administrator or developer certifications in either the Oracle or MySQL databases. That said, there are significant differences in the directions that the two databases are likely to take your career.
MySQL is a free database. It is very commonly used as part of a Web site with a database back-end. Most Web hosting services offer MySQL as an option to anyone hosting on their site. MySQL works very well for database-driven websites using PHP or equivalent application programming interfaces. Because the database is freely available, it has a huge number of small to medium companies using it. That said, because most of them are using it specifically because it is a low-cost option, many of the companies that use it may not be interested in paying for a database administrator to maintain it. There are certainly positions available for MySQL database administrators, just a smaller percentage in proportion to the number of installations when compared to Oracle. That said, developers with MySQL and PHP knowledge are in significant demand to build and maintain the websites that use it as a backend.
The Oracle RDBMS is definitely not a free database. Licensing costs for large multi-processor clusters can be hundreds of thousands of dollars annually. For this and other reasons, the companies that use it tend to have enterprise-class databases. They expect to have a dedicated database administrator to ensure their data is secure and properly maintained. The total number of installs may be lower than that of MySQL, but a much higher percentage of those will have a dedicated administrator. Of the enterprise class databases, Oracle has the largest market share and there are almost always positions available for experienced DBAs and developers.
Periodically, I check the local job listings and compare those looking for MySQL professionals to those looking for Oracle professionals. The results are interesting. As a general rule, there are a larger number of listings for MySQL, in particular for developers that also know PHP and scripting languages such as Perl and Python. However, the positions for Oracle DBAs and developers offer significantly higher salaries. That said, companies hiring for Oracle positions generally want candidates to have several years of experience. A common complaint from new Oracle professionals is that getting the first job is difficult. If you are contemplating a career working with databases, you might consider getting certified in MySQL as a way to get into the field, then become certified in Oracle as a way to move up to a position that pays more. Do not just go by this article, though. Do your own research into the local job market to see which option will work best for you.