SQL databases can now be classified under two headings like SQL databases that are purely relational and a combination of both Object and Relational.

List of relational database management systems

Major RDBMSes

• DB2
• Firebird
• Informix
• Microsoft SQL Server
• MySQL
• Oracle
• PostgreSQL
• Daffodil DB
• HSQLDB

List of object-relational database management systems

Major ORDBMSes

• Oracle
• PostgreSQL

Minor ORDBMSes

• GigaBASE [1]  ( http://www.ispras.ru/~knizhnik/gigabase.html )
• UniSQL [2]  ( http://www.unisql.com )