Many non-standard functions such as TO_CHAR and DECODE are also supported. Extensions to standard SQL include user-defined aggregate functions. Releases Several versions of HSQLDB have been released since 2001. Early versions were based on the discontinued HypersonicSQL database engine. Version 2.0, released in 2010, is mostly new code, written to conform to Standard SQL and JDBC 4 Specification. Version 2.3.2 (released in 2014) is fully multi-threaded and supports high performance two-phase locking and MVCC (multiversion concurrency control) transaction control models. See also List of relational database management systems Comparison of relational database management systems Apache Derby H2 References External links Free database management systems Java platform software SQL Relational database management systems Relational database management software for Linux Software using the BSD license Embedded databases Database engines