There are a few different aspects of working with databases: architecture and design, analysis and query construction, and of course there's the entire operational side. You'll be doing some of each no matter what and there's obviously a lot of common ground, but it'll help if you know which way you want to lean. If you have the opportunity to take a discrete math course, do so. Some resources:
Overall there's no substitute for hands-on exploration, even though databases tend to be much slower-moving than other areas (it can take a while for structural problems to become apparent, changes need to be made deliberately). In addition to being the best RDBMS available, Postgres' documentation is an excellent resource if you want to dive in yourself.
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