How to create and use Greenplum External tables?

Answer 1

The CREATE EXTERNAL TABLE command creates an external table definition in Greenplum Database. External table data is considered static (meaning the data does not change midstream during the execution of a query). This allows the query planner to choose plans that allow for rescanning of the external table data.

You may specify multiple external data sources or URIs (uniform resource identifiers) with the LOCATION clause — up to the number of primary segment instances in your Greenplum Database array. Each URI points to an external data file or data source. These URIs do not need to exist prior to defining an external table (CREATE EXTERNAL TABLE does not validate the URIs specified). However you will get an error if they cannot be found when querying the external table.

There are two protocols that you can use to access the external table data sources.
1. gpfdist
2. file