As above, Oracle is a large company that specialises in database design.
SQL is a language used in databases, and features in the names of several database systems, such as Microsoft's SQL Server. MySQL is good and free, as is postgresql.
For most jobs, MySQL and the like do their job brilliantly. Most bottlenecks are somewhere else in the system, so MySQL is chosen by many top websites, for example.
Oracle is very expensive, and is a good way to use your budget quickly. However, if your needs involve very fast database functions, then Oracle is sometimes the only place to go.
If this place you're planning on being employed by knows what they're doing, then presumably they need technology like Oracle's database stuff that is beyond MySQL. Or, perhaps they have an IT dept. that don't really know what they're doing, and think that going to Oracle will help.
A great place to ask questions like this might be stackoverflow.