ISO/IEC has released several versions of the (ANSI) SQL standard. Each is a list of requirements adopted by representatives from industry in 60 countries. ANSI, the American National Standards Institute, is the official U.S. representative to ISO. The SQL standards are implemented in varying degrees in subsequent releases from major database platform vendors.
The major vendors benefit from the standard because it partially completes requirements gathering for future releases. Their products are made of interpretations and compromises built on prior interpretation and compromise. Marketing is a factor driving adoption of standards. Why prioritize standards customers haven’t asked for?
Then there are the “disruptive innovators.” In the world of database this usually means that either: a paper critical of a standard or a vendor implementation of a standard launched a startup. Popular disruptions often find their way into the major vendor’s products.
These disruptors have been branded NoSQL and BigData. NoSQL offered document store, graph, key-value, and object databases to name a few. BigData offered relaxed concurrency for high volume high speed data. Most of these functionalities have already been included in recent release from the major vendors.
The major vendors of database platforms are IBM, Microsoft, Oracle, and SAP. IBM has DB2. Microsoft has SQL Server and Azure SQL. Oracle has Oracle, as well as MySQL which they acquired with Sun Microsystems. And SAP has SAP HANA.
These vendors offer a whole host of products in the ERP, CRM, HRM, DSS, and Analytics spaces (to name a few) most of which require a database). There are third party vendors offering Enterprise Resource Planning (ERP), Customer Relationship Management (CRM), Human Resources Management (HRM), Decision Support Systems (DSS) and Analytics Systems each of which will have some degree of preference for one of the major vendors.
What is done with data and with which software drives adoption. This is marketing engineering. Other factors that contribute to adoption is compatibility. Until recently Microsoft’s SQL Server did not run on Linux, but most every other major vendor’s software ran on both Linux and Windows. Licensing can also affect adoption. SQL Server is popular in part because of the ubiquity of Windows and Microsoft Office, each of which contribute to volume licensing requirements that lower the cost of software and support.
In my humble opinion, SQL Server, Oracle, and IBM DB2 are the best documented. Documentation should be a driver in adoption. A poorly documented system is one that is destined to fail miserably.