Add Learning SQL ebook to books (#10422)

Co-authored-by: Tom <t.baten@sigmax.nl>

books/free-programming-books-langs.md

@@ -2430,6 +2430,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Developing Time-Oriented Database Applications in SQL](https://www2.cs.arizona.edu/~rts/tdbbook.pdf) - Richard T. Snodgrass (PDF)
 * [Essential SQL](https://www.programming-books.io/essential/sql) - Krzysztof Kowalczyk and  Stack Overflow Documentation project (HTML)
 * [Introduction to SQL](https://github.com/bobbyiliev/introduction-to-sql) - Bobby Iliev (Markdown, PDF)
+* [Learning SQL](https://riptutorial.com/Download/sql.pdf) - Compiled from StackOverflow Documentation (PDF)
 * [Oracle Database Notes for Professionals](https://goalkicker.com/OracleDatabaseBook/OracleDatabaseNotesForProfessionals.pdf) Compiled from StackOverflow Documentation (PDF)
 * [Oracle8i Concepts: Chapter 15 - SQL and PL/SQL](https://docs.oracle.com/cd/A87860_01/doc/server.817/a76965/c14sqlpl.htm#5943) - Lefty Leverenz, Diana Rehfield, Cathy Baird (HTML)
 * [SQL For Web Nerds](http://philip.greenspun.com/sql/) - Philip Greenspun (HTML)