OCaml may be used when you need to write a safe program (as it is a functional language). It's quite easy to learn, almost no syntax.
An incomplete (in-progress) course about C++.
Relational databases are using SQL (89 or 92) as their query language. Since ~2011, NoSQL databases are more and more used.
If you want to add functions in SQL, you need to learn the Procedural Language (PL) for SQL. In PostgreSQL, this is called PL/pgSQL.
Learn about NoSQL 'NotOnlySQL', 4 new kinds of databases which are more flexible than relational databases (such as MongoDB or Cypher).
How to start, what you need to know, ... and everything that couldn't be put in a specific language course.
A complete summary of what you need to know in HTML to make a website.
What's CSS and how you could use it to make your website looks better.