H2 HSQLDB Derby

H2 and HSQLDB are different database

H2 official website: http://www.h2database.com/html/main.html
H2, the Java SQL database. The main features of H2 are:

•Very fast, open source, JDBC API
•Embedded and server modes; in-memory databases
•Browser based Console application
•Small footprint: around 1 MB jar file size

Features
H2 Derby HSQLDB MySQL PostgreSQL
Pure Java Yes Yes Yes No No
Memory Mode Yes Yes Yes No No
Encrypted Database Yes Yes Yes No No
ODBC Driver Yes No No Yes Yes
Fulltext Search Yes No No Yes Yes
Multi Version Concurrency Yes No Yes Yes Yes
Footprint (jar/dll size) ~1 MB ~2 MB ~1 MB ~4 MB ~6 MB

see http://www.h2database.com/html/features.html#comparison
fore more detail comparision.


HSQL Official website: http://hsqldb.org/
HSQLDB reference:
http://www.cnblogs.com/fyfblog/archive/2010/12/10/2097149.html
http://www.blogjava.net/willpower88/archive/2006/11/29/84369.html
下载了HSQLDB后，hsqldb-2.2.9\hsqldb\doc\guide下有详细文档，doc下还有其它一些帮助文档