Working with File-Based External Tables
External tables provide access to data stored in data sources outside of HAWQ as if the data were stored in regular database tables. Data can be read from or written to external tables.
An external table is a HAWQ database table backed with data that resides outside of the database. An external table is either readable or writable. It can be used like a regular database table in SQL commands such as
INSERT and joined with other tables. External tables are most often used to load and unload database data.
Web-based external tables provide access to data served by an HTTP server or an operating system process. See Creating and Using Web External Tables for more about web-based tables.