SQL background/history:

IBM invented a computer language back in the 1970s designed specifically for database queries called SEQUEL, which stood for Structured English Query Language. Over time the language has been added to, so that it is not just a language for queries but can also be used to build databases and manage security of the database engine. IBM released SEQUEL into the public domain, where it became known as SQL. Because of this heritage you can pronounce it as “sequel” or spell it out as “S-Q-L” when talking about it. Various versions of SQL are used in today’s database engines.

Microsoft SQL Server uses a version called Transact-SQL.

Microsoft initially developed SQL Server (a database product that understands the SQL language) with Sybase Corporation for use on the IBM OS/2 platform. Oh what a tangled web we weave! When Microsoft and IBM split, Microsoft abandoned OS/2 in favor of its new network operating system, Windows NT Advanced Server. At that point, Microsoft decided to further develop the SQL Server engine for Windows NT by itself. The resulting product was Microsoft SQL Server 4.2, which was updated to 4.21. After Microsoft and Sybase parted ways, Sybase further developed its database engine to run on Windows NT (Sybase System 10 and now System 11), and Microsoft developed SQL Server 6.0—then SQL Server 6.5, which also ran on top of Windows NT. SQL Server 7.0 now runs on Windows NT as well as on Windows 95 and Windows 98.

SQL Server developed  using : C,C++

SQL Server release history:( As per Wikipedia)

In 1988 Microsoft joined Ashton-Tate and Sybase to create a variant ofSybase SQL Server for IBM OS/2 (then developed jointly with Microsoft), which was released the following year.[5] This was the first version of Microsoft SQL Server, and served as Microsoft’s entry to the enterprise-level database market, competing against Oracle, IBM, and later, Sybase. SQL Server 4.2 was shipped in 1992, bundled with OS/2 version 1.3, followed by version 4.21 for Windows NT, released alongside Windows NT 3.1. SQL Server 6.0 was the first version designed for NT, and did not include any direction from Sybase.

Version Year Release name Code name
1.0 (OS/2) 1989 SQL Server 1.0 (16 bit) Ashton-Tate / Microsoft SQL Server
1.1 (OS/2) 1991 SQL Server 1.1 (16 bit)
4.21 (WinNT) 1993 SQL Server 4.21 SQLNT
6.0 1995 SQL Server 6.0 SQL95
6.5 1996 SQL Server 6.5 Hydra
7.0 1998 SQL Server 7.0 Sphinx
1999 SQL Server 7.0 OLAP Tools Palato mania
8.0 2000 SQL Server 2000 Shiloh
8.0 2003 SQL Server 2000 64-bit Edition Liberty
9.0 2005 SQL Server 2005 Yukon
10.0 2008 SQL Server 2008 Katmai
10.3 2010 Azure SQL DB Cloud Database or CloudDB
10.5 2010 SQL Server 2008 R2 Kilimanjaro (aka KJ)
11.0 2012 SQL Server 2012 Denali
12.0 2014 SQL Server 2014 SQL14
13.0 2016 SQL Server 2016

Note:  Microsoft negotiated exclusive rights to all versions of SQL Server written for Microsoft operating systems.

In 1996 Sybase changed the name of its product to Adaptive Server Enterprise to avoid confusion with Microsoft SQL Server. Until 1994, Microsoft’s SQL Server carried three Sybase copyright notices as an indication of its origin.

Good Reference: https://en.wikipedia.org/wiki/Microsoft_SQL_Server