Standard Query Language / SQL
SQL is a language for talking to relational database management systems. If you have a database involved in your system then you likely will have to include some SQL in your application along with whatever other language you write it in.
💬 Codecademy actually has a pretty good interactive SQL tutorial.
Oracle’s extension of SQL to include procedural language as well.
PostreSQL version of SQL roughly similar to PL/SQL in some respects.