Perhaps the most common external source of data is from relational databases. Since this section is probably of interest to only those who work with databases—or at least plan to—some knowledge of the basics of relational databases is assumed.
One way to connect to databases from R is to use the RODBC package. This allows one to access any database that implements the ODBC common interface (for example, PostgreSQL, Access, Oracle, SQLite, DB2, and so on). A more common method, for whatever reason, is to use the DBI package and DBI-compliant drivers.
DBI is an R package that defines a generalized interface for communication between different databases and R. As with ODBC, it allows the same compliant SQL to run on multiple databases. The DBI package alone is not sufficient for communicating with any particular database from R; in order to use...
