Kia ora katou! :}
And welcome to LQ!
The question is a bit vague, and not really Linux specific.
SQL is a "structured query language" that you use to extract,
update, insert or delete information that is stored within a
RDBMS with ... interbase and SQL are *NOT* interchangeable,
interbase just happens to be a RDBMS. For other OpenSource
database systems have a look at e.g.
http://www.postgresql.org
(which is my personal favourite, and one of the most complete
FOSS databases - for a discussion of the virtues of the different
RDBMS' out there have a look at our members choice award [note: a
high number means popularity, not quality ;}]).
[edit]http://www.linuxquestions.org/questions/showthread.php?t=409045[/edit]
Cheers,
Tink