1. SQL is not a proprietary language used by specific database vendors. Almost every major DBMS supports SQL, so learning this one language will enable programmer to interact with any database like ORACLE, SQL ,MYSQL etc.
2. SQL is easy to learn. The statements are all made up of descriptive English words, and there aren't that many of them.
3. SQL is actually a very powerful language and by using its language elements you can perform very complex and sophisticated database operations.