Added two SQL books (#3555)

Author: TimoSalomaki

free-programming-books.md

@@ -2551,6 +2551,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Developing Time-Oriented Database Applications in SQL](https://www2.cs.arizona.edu/~rts/tdbbook.pdf) - Richard T. Snodgrass (PDF)
 * [SQL For Web Nerds](http://philip.greenspun.com/sql/)
 * [SQL Notes for Professionals](http://books.goalkicker.com/SQLBook/)
+* [SQL Queries Succinctly](https://www.syncfusion.com/ebooks/sql_queries_succinctly) - Nick Harrison
 * [Use The Index, Luke!: A Guide To SQL Database Performance](http://use-the-index-luke.com)
 
 
@@ -2573,6 +2574,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [SQL Server 2017 Administrator's Guide](https://www.packtpub.com/free-ebooks/sql-server-2017-administrators-guide) - Marek Chmel, Vladimír Mužný (Packt account *required*)
 * [SQL Server Backup and Restore](http://www.red-gate.com/community/books/sql-server-backup-and-restore) - Shawn McGehee (PDF) (email address *requested*)
 * [SQL Server Execution Plans, Third Edition](https://assets.red-gate.com/community/books/sql-server-execution-plans-3rd-edition.pdf) - Grant Fritchey (PDF)
+* [SQL Server for C# Developers Succinctly](https://www.syncfusion.com/ebooks/sql_server_for_c_sharp_developers_succinctly) - Sander Rossel
 * [SQL Server Hardware](http://www.red-gate.com/community/books/sql-server-hardware) - Glenn Berry (PDF)
 * [SQL Server Internals: In-Memory OLTP](http://www.red-gate.com/library/sql-server-internals-in-memory-oltp) - Kalen Delaney (PDF)
 * [SQL Server Metadata Succinctly](https://www.syncfusion.com/ebooks/sql-server-metadata-succinctly) - Joseph D. Booth