В книге "Inside Microsoft SQL Server 2000" авторов Ron Soukup и Kalen Delaney кратко описана история создания MS SQL Server'а.

SQL Server: The Early Years
In 1986, Microsoft was a mere $197-million-per-year business with 1153 employees. (Ten years later, Microsoft had revenues of nearly $6 billion and almost 18,000 employees.) Microsoft's products were entirely desktop focused, and the main bread-and-butter product was MS-DOS. Client/server computing was not yet in the vernacular of Microsoft or the computer industry. Data management on PCs was in its infancy. Most people who kept data on their PCs used the wildly popular Lotus 1-2-3 spreadsheet application to keep lists (although many were discovering the limitations of doing so). Ashton-Tate's dBASE products (dBASE II and the recently released dBASE III) had also become popular. Although a few other products existed, such as MicroRim's Rbase and a relatively new product from Ansa Software called Paradox, Ashton-Tate was clearly king of the PC data products. In 1986, Microsoft had no database management products. (Beginning in 1992, Microsoft would go on to achieve tremendous success in the desktop database market with Microsoft Access and Microsoft FoxPro.)

IBM's Database Manager wasn't in the same category as products such as dBASE, Paradox, and Rbase. Database Manager was built to be a full-featured database (with atomic transactions and a full SQL query processor), more similar to traditional minicomputer-oriented or mainframe-oriented systems such as IBM's DB/2, or Oracle, or Informix. Microsoft needed a database management system (DBMS) product of the same caliber, and it needed one soon.

Microsoft turned to Sybase, Inc., an upstart in the DBMS market. Sybase hadn't yet shipped the first commercial version of its DataServer product (which it would do in May 1987 for Sun workstations running UNIX). Although certainly not a mainstream product, the prerelease version of DataServer had earned a good reputation for delivering innovative new capabilities, such as stored procedures and triggers, and because it had been designed for a new paradigm in computing: client/server.

As is true in all good business exchanges, the deal between the two companies was a win-win situation. Microsoft would get exclusive rights to the DataServer product for OS/2 and all other Microsoft-developed operating systems. Besides getting royalties from Microsoft, Sybase would get credibility from Microsoft's endorsement of its technology. Even more important, Sybase would gain a beachhead among the anticipated huge number of personal computers that would be running the new OS/2 operating system.

Ну а далее они описывают как и почему MS и SyBase разошлись.

Книжка, кстати, вышла в издательстве Microsoft Press, так что обвинить авторов в лукавстве сложно.