SQL is used to interact with Database Systems. As per ANSI (American National Standards Institute), SQL is the standard language for Relational Database Management Systems.
SQL has been the prominent language to interact with various Database Systems for many decades. While many languages that existed two decades ago are extinct now, SQL has always maintained its supremacy in the RDBMS world. Over the time, it has only advanced with new features and standards. And it seems to stay that way for years to come.
About Oracle Database:
Oracle Database is one of the prominent Database Systems in the RDBMS (Relational Database Management Systems) segment. Some of the other prominent Database Systems are
- Microsoft SQL Server
- MySQL
- Sybase ASE.
They also use SQL to interact with their Database Systems. While there are subtle differences between each of their SQL implementations, a SQL as a whole, is generally very standard. So a person with SQL knowledge in one platform such as Oracle, may find it easier to learn and code for other Database Systems such as Microsoft SQL or MySQL.
The point is, once you learn SQL, then your reach into the job market is very wide.