Here is a link to some practice problems on manipulating data frames in R: More Practice with Data Sets.
There is no separate dataset to download. The practice problems follow the UCLA slides pretty closely starting at “Modifying Data”.
Happy coding!
I just found mention of a package that allows using SQL (database) syntax to join data tables together, sqldf(): http://crantastic.org/packages/sqldf
The reference was at http://stackoverflow.com/a/1307824
The documentation for sqldf() also gives examples for both SQL and non-SQL versions of several join operations.
This ppt presentation might be helpful for folks comparing SQL, merge and data.table options: files.meetup.com/1406240/Data munging with SQL and R.pdf