Hi

Check below links :

http://en.wikipedia.org/wiki/Join_(SQL)

http://msdn.microsoft.com/en-us/library/zt8wzxy4.aspx

http://www.dotnetuncle.com/sql/What-is-Join-in-SQL-types-of-joins.aspx

In all databases the function of join is same including crystal.

Usage is based on business or report requirement.